NEW fuel pump, a 044(group a) pump would be best.
Your ideas seem sensible, but personally I would ditch the ecu, and run aftermarket of your choice, just don't pay for a big name, launch control might be an advantage ?, with what you're doing.
Add front and rear strut braces, rear brace ideally needs triangulating to the floor, braided brake hoses decent pads, if getting larger wheels get bigger brakes too, could convert the rear discs to vented, 4x4 cossie rear calipers discs fit straight on.
2 VERY common failure points on cossies are the fans and fuel pump, this is due to the age of the wiring on the fuel pump circuit, and the fan circuit was a disaster to start with, fuses/relays/wiring burns out, so these two need rewiring, even for the road, then decide what spec you want the engine, for 420 you don't need to lower the compression ratio at all, I would suggest a T38, roller bearing if you get it, with a BD14 inlet cam, leave the std exhaust cam it is fine, head porting will pay massively well and can gain you everywhere not just at the top end but low down also if done correctly.
tabetha