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 drive it right you could probably get 42 and up in town.
Mucho parts for those ALH engines and getting 140 to 160 HP is a snap, still retaining the mileage. Originally it was 90 HP.
Stay away from the 2004 and up PD engine, as that was someones wet dream of how to squirt diesel into a engine.
I have a spare 2001 ALH that we are going to make a set of headers, Intake and exhaust system for my 2003 Jetta.
Used TDI engines are sort of pricey.