Being a newbie myself who got into these cars for the same reason you are, but for transplant into a 96 rover, I can tell you the main difference.

82 up the engine was reenforced and turbo was added. 81 and older are naturally aspirated. You will want to go with an 82 or newer and have the turbo... Especially in a heavy 4x4....

On parts... Cheap and everywhere. Replacement engines, cheap and everywhere. Great platform, super easy to work on. No computers etc... Has become my single most favorite engine I have ever played with.