I have a 68 with a 302 v4 automatic! Im finding deals on gt40 crate motors for fox body mustangs that ar 50 oz balanced soooo is it just a matter of finding a 50 oz flexplate with the proper amount of teeth to match the c4 tranny???
You can bypass the timing cover change and run an electric fuel pump. But PLEASE run a circuit so that the pump only runs when the starter is activated or that the engine is running like using alternator feed and diodes.
I had my '68 C4 flex plate rebalanced to match the balance of 5.0L flexplate. The balance shop welded a rectangular weight and progressively drilled out material until it matched. If you keep the serpentine belts, you'll have to use a radiator (or have your's modified) with the lower neck on the driver's side.
5.0L water pump exits to the driver's side, '68 302 water pump exits to the passenger side. I'm running the stock V belts with a '68 water pump. I had to have a custom aluminum crank pulley machined to line up with the 3 accessory V belts. The front surface of the 5.0L harmonic balancer sits slightly FWD compared to the '68 and it has a 4 bolt pattern. You also MUST use a billet steel distributor gear with billet steel roller camshaft. An '85 5.0L Mustang/Capri Duraspark II distributor is the only stock distributor that comes with a billet steel gear with the correct inside diameter. The 5.0L EFI steel distributor gears have a larger inside diameter.