Any engine swap is possible in the auto world...but is it worth it?
I know a guy with a GM Crate 502BigBlock in an old GMC front wheel drive RV - Very Cool!
Besides the change of all the mounts (requires a metal fab project), the newer engine/tranny sets are fully computer controlled, so would need the entire electrical loom from a donor vehicle
- and - the fuel delivery system has to be changed for the high pressure injection system (often a loop system that has a high pressure return line). The gearing in the axle might need to be changed too (depending on the original ratio).
It is generally accepted that an engine swap from old tech (carb) to new tech (Fuel Injection) would cost starting
at 4 times the cost of a rebuild of the original motor.
Upgrading the original motor and tranny with heavy duty parts, plus adding a Gear Vendor over/under-drive is often less expensive and easier for a DIY type owner.
Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.
And finally with RV's, the cost of doing an engine/tranny swap often makes upgrading to a "new-to-you" gently owned unit a better deal.
Hope that helps.