I'd be changing out the whole engine, not messing with the original so I could go back if I chose to. It's a 5.0 as it stands, but I don't want to mess with a carbed engine. I'm a sissy like that.If its all original then it would be a shame to mess with it.
Are you looking for more power or better fuel economy.
For ease of finding an engine with all of the associated parts like the loom and engine management systems for injection then your probably best to get the 5.0 liter out of an AU Falcon.