Woody, all depends what you want from your new engine.
Is it for more power, more economy etc
These question will give you an idea as to what engine to choose.
Any engine will fit, its just some fit easier than other.
As winchman says vauxhall is a very popluar fit, although in a vit a little more difficult than an sj.
Id say the isuzu 1.5 would be a bit underpowered for a vit, maybe the 1.7td, or a 1.9td peugeot engine if diesel is what you want.
There is a very big selection of engines you can fit, its just a case of picking one that does what you want from an engine, and is relativley easy to fit