LOL 2.16 square meter frontal area, noisy under car floor pan, .39-.40 Coefefficient of drag. That takes the HP it does to shove down the road/thru the air with the alignment settings it does to make it fly straight with the suspension it has for whatever rolling resistance that is.
No matter what powers it, it takes ~20HP just to go 60mph, the Honda insight takes 10-11hp. Increase the MPH over 75 & the power starts to get ugly/closer to 30-40HP/not likely lean burn cruise or out of boost on the 2.3L redblock with the chassis rolling resistance & aero drag/noisy under car parachute rear bumper.
+ tractor engine from 1961 with ever larger displacement but same stroke/crank/bearing journal dimensions carried over from the pushrod tractor, alum head & updated FI (tho it's been basically the same LH jet (ish) since 1981-1982 LH1.0 with a lot more ignition resolution for knock detection/off idle grunt in the LH2.4-3.1+ starting in 1989 or regina FI on the 7/9 49-state automatic cars...
As to the 960 (you swapped in the 3.31 rear axle in the 940 Turbo that originally had 3.73s with the AW-71? That must drive awesome.
), with stock sized tires, the 3.31 would be absolutely ridiculous/useless with a lock-up torque converter. The only reason the MPG is maybe any better at (75+?MPH?) is either selected cruising speed speed in the flat (absurdly high/highway mileage is likely to suck, anyway) or slippage/torque multiplication through the converter (though, lord knows how much heat or wear/tear that's creating or strain its putting on the engine to lug it like that).
With the .69 OD ratio & stock sized tires the AW71L w/4.10s cruises about the same RPM as the absurdly tall 8V N/A USA 2.3LEFI cars '83+ that have 3.31s with the manual & .80 OD ratio. They kept the RPMs low with real mild torque/grunty smogger cams compared to the B20E D-cam not so much for MPG as to keep from stirring up all that naughty naughty gross oil windage from the crankcase for unburned HCs or NOX burning at light load real lean for federal/CARB steady state flat ground 55mph cruise emissions tests standards sniffing the tailpipe. This was NO joke for tighter emissions #s by 1995 for the tractor redblock...they had to put a LOT more exteral bandaids on them 1994-1995 for CA-emissions steady state 55mph flat cruise standards as well as passing simulated dyno tests every other year in the strictest area (los angeles/valley smog).
This said, the D-jet super lean burning high compression '71 140E or 1800E uses about the same amount of fuel with same diameter (though skinny 165R15 tires, originally) w/4.10s & no OD/M40 or M41/M410 w/.79 OD ratio in good repair, even screaming along at 4000RPM. Less weight/fewer accessories or electronics to babysit too! Burns real lean, 2700lbs or less for a stripper 140, ~2500-2600 depending on options for an 1800E, motor can spin along at 70mph just fine, but won't pass 1975+ emissions or run that well without hardened valve seats/other upgrades to run on modern oil & fuel/lead free gas.
The brick shaped car with the over-stressed tractor engine originally conceived in ~1958 with some blower/supercharger (clutched or not) kludged onto it & lousy aerodynamics/noisy under-car isn't likely to sip fuel or drive all that well compared to modern, even with a programmable early electronic controlled 03-71LE from the N/A previa recombined with Volvo shafts/bellhousing for a bolt-in solution or even machining the only *slightly* newer tech 4-speed A340/AW4 family trans into it going to all that effort to install something that's still a dinosaur by modern standards...
If you want more torque & a little less aero drag, they did sell 3.0 facelift 960s with said A340 / AW30-40LE as Volvo calls it, though IIRC all 1995+ models are CA compliant & 1998-only models got the air pump + EGR for CA? if I remember well?
They're not much smoother underneath with actual air guides, nor are P80 850/70 series, but a little bit with the transverse leaf IRS instead of the solid rear axle.
Much that is electrical to fail, much interior plastic to fall apart, glass sunroofs (or any sunroofs I hate), power seats, fewer years interior parts interchange, smooth bumpers instead of black bumpers to bash around.
I stick to 145EFI manual window/no sunroof cars or 245 manual window no sunroof cars no airbag (tho I do like ABS brakes & LH3.1 last version of the FI & sound deadening 1989 stiffer chassis/better sound deadened/better rustproofed/less cabin or windshield water leak prone models , but old style ignition switch/manual windows still & single stage paint more common (white, 190 yellow, 213 blue etc still used -'89 & I like to delete the 3rd brake light (early hatch glass swap)/less in the hatch harness to fail on me/how cheap (that's frugal, to you!) can I be?).
They also sold AW71L N/A 940s here with a pretty strong trans that holds up to turbo power in stock form, but not with the 940T stall speed lockup torque converter & shift points like the Canadian 1993+ 940Turbos got to make it a little less terrible to drive with the super lazy N/A 940 shift points & slow stall speed torque converter...the 1993+ Canadian 940T in good repair with the AW71L & 4.10s was good for an honest 2mpg highway in 49-state lean burning form. Won't pass SoCal super tight NOX requirements as cleanly, especially the steady state 55mph cruise test, however. Torque converter & valve body for a USA N/A AW71L fits in a large flat rate box or can be picked up at the canadian border? IDK? BTDT? Nice junk drawer recombine to get a little better acceleration & MPG & less heat from the slipping non-lockup torque converter at light throttle cruise in OD for better longevity (tho more complexity/failure parts (torque converter clutch), but TCC seems to give long life if cared for on 03-71L & 03-71LE (I got 500,000 miles out of one in an N/A previa w/much towing in 3rd+locked converter).
The last of the redblock tractors N/A 940s for CA emissions had the turbo sized much larger cat converter (& volvo probably only wanted to use up the last of 1 type for a model they were phasing out in the USA market), pulse air injection & EGR to squeak them through emissions with their old bathtub combustion chambers & LH EFI engine management.
They sold redblocks rest of world up to 1998, but they weren't USA OBDII style emissions compliant...