Yeah, they see themselves standing on the side of the road , in the middle of nowhere without cell service waiting for a tow truck.
Yeah...but I'm often amazed at the reluctance that many Americans (I do not know how people in other countries feel about their own countries) have to just get out and drive. There's not going to be any interstate highway between Tuscon and Philly that does not have pretty robust cell service. Back roads, sure...but if you use your head, you're not going to do things like drive through the San Carlos reservation in a 40 year old untested car (yeah, I've been there..and they actually DO have cell service even there, it's just a lot sketchier than what you'll find on I10.). But my real point is that as long as the car runs and is basically safe (stops, has lights, etc.) there's no hazard driving it just like you're going to once you get home. We live in such a developed country...it surprises me when people are reluctant for safety reasons to go out and experience it at eye-level.
The biggest problem you'll encounter is being passed by a constant flow of semis and other cars. So if you do break down, someone will be along in short order. Well before you get devoured by coyotes and armadillos
I speak from experience having driven last August a rust-free 1976 245 that I bought in Albuquerque and brought back home to Boston. Roughly equivalent to your contemplated trip. My car had around 280K (more now
) and I did what you're doing now...getting it checked out by a reputable Volvo shop before heading out on the road. We replaced a fuel injection relay, put on a new set of wires and plugs, and were good to go. I did replace the tires before heading out as (has been said here) there's just no accounting for what might happen with old rubber. I carried a spare timing belt and tensioner, a bunch of radiator hoses, and alt belt. All of these still reside, un-used, in the trunk as they were not required on the trip. And a basic tool box (which wasn't trouble to carry on the flight out to NM). We could have probably picked up the tools in Walmart if we had wanted.
4 days on the road, with my freshly-minted driver kid, and it was a great trip. And while we had sore butts after 2500 miles behind the wheel (those 42 year old seats were among the first things to be replaced in the car), we pretty much always had cell coverage if we needed it. I highly recommend it. Go for it!
(the kid, by the way, pointed out that we could have just slept in the back of the car...but hotels and friends' beds were one geezer concession I insisted upon)