#1 -- I can't believe that you or anyone (Mario) would start with bodies that are so rotted out! OMG! But I also understand it. Not dissing you or anyone else that's had to go thru this. Just saying - it's amazing how much work and $$$ has to be spent just getting back to 'standard'.
#2 -- Great project. Taking it on in the UK even more outstanding!
#3 -- IMHO -- just get a nice GM crate motor - LS7 is 'more than' ample - LS9 if you want to scare yourself and spend a bunch more... I would think sticking with a standard crate motor and standard computer to run things in the UK would be a huge advantage. Dress it nicely and you'll have a great car.
#4 -- Commenting really just because I wanted to subscribe! So pay no attention to #'s 1 thru 3