75-8 efi looks pretty easy to retrofit into earlier zcar. I had to pull the harness out of mine to figure out what was going on with it, and in the process figured out how it works. one wire to (-) post for injector pulses and tach, hook up the water temp sensor correctly and run some grounds, the other parts of the harness that need power are part of the battery harness and one ACC power source, the ecu uses a two in one relay to control the fuel pump and turn on efi, and thats about it, if all the other sensors and parts are in good working order. Pretty simple. Easier than turbo conversion, and turbo conversion is easy. 75-6 tank bolts straight into early zcars, on a 70-71 you need the mounting strap from the 75-6, on 72-74 it will bolt straight in with the original moutning strap. I would do this before making surge tank just because its pretty simple and these tanks are not hard to find in Norcal. I kinda like SU carbs for a simple NA motor, easy to work with and they have been pretty reliable to me in my experiences with them.