fuelinjection is a hard one to answer, you can get a SDEFI setup that drives 8 injectors and runs a distributor for arround 650 US, There is a french sysyem called sybele that can run eight injectors, bank to bank, and wasted spark ignition, and that system is about 750 US, all you would need then is the 75-78 efi manifold of a 472/500 caddy, it allready has injector bungs etc and with porting etc. you should be just fine, that is about the cheapest way to go.
Alternatively you have to fabricate a manifold with one, or even better two plenums (that way you can make a hemholz resonator to add horsepower) and add two latemodel mustang throttlebodies and weld in some injectorbungs and make a fuelrail etc. its all within your abillities and all it requires is time. you can mail me at firstname.lastname@example.org and i can help you out with the hemholz/ tuned runner length. (sorry kultuz, its just that this is actually real mechanical engineering)
anyway keep us posted on developments