Another question on the Volvo.

Background:
It's got a T9 transmission swap, so I don't know for sure what's in it overall. It appears to be an early style driveshaft, as the support is held up by two rubber bushings with pins through them.
The u-joints are pretty small and apparently I've already cracked one in 5000 miles of driving (and that was before I took the car apart to re-engineer the swap that was started when I bought it...)

Questions:
what changed in the drivetrain over the years, most specifically in respect to the 1965 models and later years? Can I use a later driveshaft without significant re-working? Especially because I have a swapped transmission and until I get home (2 weeks...) I won't know the details on how exactly that swap was completed (custom yoke to Volvo u-joint? conversion u-joint? redrilled for flange-to-flange adapter?). I see the 1967 or so and up vehicles used a larger u-joint which looks like it might be compatible with the '80s Ford u-joints?

Thanks!

Ben

P.S. While we're at it...anyone got a measurement from the firewall (specifically the front of the heater box) up to the radiator, and another from the heater core outlet over to the inner corner of the battery box? I'm thinking of making a little bent tubing for my coolant return and I'd like a guess at how much to order...