[olddog]

Are you in the UK? Where are you located?

Not knowing the maker of the car doesn't help much either.

Is this a 427 body or a replica of a small block car?

As far as engines go, the original SB cars had 260 and 289 engines, and the BB cars had 428 and 427 engines. For value the closer you stick to the original the better. In reality there are more 5.0 block engines stuck in 427 body replicas than there are 427 engines, and even more 351 Windsor blocks (based on the London Cobra show over the years).

Putting a stock 5.0 in a Cobra is pretty boring by most standards and would not impress very many potential buyers. It would work just fine, but it is not a strong engine. As far a resale value goes, I do not think there is a hill of beans difference between the 289 carb and the EFI 5.0. It's personal preference. Replacing the auto with a manual will be a step up in most minds.

Some people like fuel injection, some don't. You see more carbs. EFI is much more expensive to install. You start modifying the engine to make decent (400 Hp) power and you end up replacing just about everything to supply enough fuel to it.

Here is a free tip. The 94 & 95 Mustang have a totally different control strategy in the ECU, and it requires much more skill to tune, with engine modifications.