Yeah, i would say the same with the old a12. They go hard but im always looking for a bit more.
Im not quite sure what you're looking for, any engine swap will take work, time and money...
Anything engine other than a series will need cross member mods and engineering, i would say a14/15 would be your best bet! Easy to work with, relatively cheap, sound awesome and pretty darn reliable too!
I would say a couple grand would be spent in order to get good hp, you could fuel inject and turbo it too if you dont want to for carbies. Or use fuel injection throttle bodies...
You mentioned "old school rally look" does this mean you're only going for the look or you're planning on rallying it?