Engine swap

Stock had beefed up fuel injectors that probobly added to these specs.

1991 Mustang GT, Horsepower: 225, Torque: 300

Carberated would not put out as many ponies. I am also not sure of the manifold or harmonic balancer swap. My cousin put an injected motor like this in an older car but went with the injection and serpentine belt. Come to think of it they do make kits to convert V belts to serpentine so there should be V belt balancers that fit the cranks. It might not be the 68 harmonic balancer but there should be ones that fit.

Finding answers can be the hard part sometimes. the way the 302 oil seal is on the harmonic balancer would be hard to figure from the crank and balancer specs, so finding someone that has tried it would be the best bet. Your local high performance shop mechanic would probobly know.
The heads on the 91 GT were origonally designed for the 302 truck engine. It has been a long time since I had the intake off one but think the ports were bigger and more vertical on the fuel injected motors. This could be checked by just comparing pictures of the manifolds. Though even if they do look the same the bolt pattern may be different.
Then there are books and magazine specifically for engine swaps. And if you do not want to pay most bigger libraries have alot of automotive service manuels, parts books, etc. etc. etc. or "How to build a small block Ford"

you need some more experts i didn't learn a thing from this answer : can i put the 1968 harmonic balencer on the 1991 5.0 ? is there balance differences in the engines that requir different harmonic balencers? Can any one direct me to people who do have the answers to my questions ?Thank you Tom Putnam