Some mods I made to my '91 Yota 4wd work truck:
Deleted the v6 gas engine; replaced with 4 cylinder VW TDI.
I suppose I saved some weight there...
Upgraded the intake and exhaust manifolds.
Upgraded the turbo to one from a Mercedes Sprinter van.
Upgraded the injection pump.
Upgraded the fuel injectors.
Upgraded to a BIG intercooler.
Upgraded to a BIG electric cooling fan.
Deleted auto tranny, replaced with 5 speed manual.
I suppose I saved some weight there...
Deleted the AC system
Deleted 1/2 of the exhaust system. It breaths much easier and is lighter.
Deleted the old copper radiator; replaced with aluminum.
I suppose I saved some weight there; it does run a bit cooler.
Deleted the ADD 4wd system and replaced with manual locking hubs.
Deleted some interior bits that were in the way of the shift levers.
Deleted 1/2 of the front bumper - the useless facade half.
I still run big mudder tires on it, and also have a ladder rack and a big toolbox.
It can also pull pretty heavy loads, like a loaded horse trailer or a car hauler full of hay.
In the end, the diesel is very torquey, but don't expect to go fast.
However, the fuel economy is 35% better than the stock v6/auto tranny AND I'm running biodiesel.