The engine you want is a 99.5 to 2003 1.9 TDI from a Jetta or Golf. You might want to stay from the 99 computer as they had a few issues there.
Motoring that brick (Samurai) around, if you gear it to be at 2000 to 2200 RPM at 60 to 65 it should get 32 to 38 on the highway and if you learn to...