This is probably more a maintenance thread, no?
You're just trying to make it work at all (and last a while?) for as cheaply as possible with no adaptation?
Mods move?
How cracked is the turbine housing?
A couple small ones on either side of the puck is usable, cracked all the way through the snail you probably have to pitch. See stealthfti pbase picture gallery..
Easiest/cheapest for bolt-on with no custom oil/water lines on the b21ft is just a T3 off a 700, with either the 240 .63 exhaust housing or the 700 .48. 700s have a 50 trim compressor, 240s a 45.
If it’s staying totally stock/non IC, letting the heat out of the loop with the .63 exhaust and having a compressor that’s efficient at 6psi (such as the 45trim it came with) is probably a good thought, much like the factory did very conservatively from new. Though the 700 50 trim compressor for intercooled use isn't really radically different.
This said, turbos have come a ways in 30+ years (to say the least).
Even if you’d like to stick with an old T3 (if you can find a rebuild-worthy example or recently replaced used example on a 700 that has all the volvoid bits, including the turbine housing lip), either the cosworth style (best of the T3) or atp style wastegate really help them out for cheap/bandaid/simple internal gate solutions. If you insist on stock dp/flange, even the 700 watergate housing with the larger puck and porting the wastegate hole in the turbine housing as well as porting the housing/outlet with the carbide bit / mill a little helps considerably if you’ve got more time than money and/or the DP constraint is critical.
If intercooled with a better intercooler, 60 trim compressor off the ford/merkur machined into the Volvo compressor housing so it fits like stock is nice.
Works well with any of the milder cams that still idle smooth/give good torque like the T, stockish 8V head etc. Water fittings (if it has them) are different as is a fair bit of the hardware on the ford center section (I try to use the Volvo center when possible just for no fuss fit).
If using the ford center:
Swap the Volvo turbine housing on
or machine Volvo Manifold flat to use the ford/more generic T3 style turbine housing
or use the rare 1981 240t manifold that doesn’t have the lip.
Figure out the water lines if it has them (maybe just the fittings are different, but I want to say the ford are pipe thread instead of the metric banjo there the volvoid app uses (sorry for the quasi-hearsay, it's been a minute since I've recombined this particular junk pile to fix old beat up Volvos)), oil are the same style/compatible.
Some nissans got the 60 trim, though their .42 compressor housing isn’t identical in external fit to the Volvo. No fun to dig those out and those cars mostly are all in the crusher by now. Battery sawzall and really strong tin ships are your friend with those dreadful cars to extract the turbo. Iirc the Volvo uses a different style seal on the compressor, forget it 700s do but iirc they do that with the restriction or the kjet plate in mind. Some Audi 5cylinder turbo cars got T3s as well, as well as the D24T. Most of those have a metric banjo for the oil feed, not sure they'll accept the 2-bolt volvo feed, I forget.
TD04s are plentiful and cheap, though a lot of them are rather tired out by now on the in-out play and ready to let go pretty soon and no one ever replaces them since it’s expensive/ relatively time consuming and the whole FWD car/engine is usually ready for the scrap by now if it’s P80 and earlier.
And you’d be embarking on an adaptation for time and all
That. You can almost get one of those miserable things to flow as well as the cosworth .48 (prefer the rare .63, lag not bad really and I’m more longevity oriented/want to keep it out of boost at cruise / don’t have electronic boost control of a modern car) if you port them out a ton and use s late angle flange version and find a good used minty 16T/18T/19T for dirt cheap and do all the adaptation at .17c/hr. I machine the compressor shape from the 16T/18T/19T housing into the 13C housing, but at the time it was inexpensive enough to do that and meant no hooptie brackets for the waste gate
Maybe someone makes a bracket that isn't super flimsy by now that slips under the boost signal line nipple somehow on the FWD housing to at least hold the WG actuator on there a little more securely by two spread out points around the housing. Some people use a T3 actuator to that effect more or less...
Rather recombine the T3 junk pile, old as it is, and annoying as the (now usually frozen) bolts into the turbine housing arrangement instead of the v-band and indexing pin the Mitsu junk uses not have he super restrictive exhaust of the TD04s and better longevity with lots to recombine, slower shaft speeds/margin of safety to run continuous boost to climb over mountains / cruise with better economy/less heat backed up, but personal preference.