Power and Efficiency

[Rileys68Camaro]

The old engines are worse on gas, but you can help by adding fuel injection or if you can afford it, install a LS1 engine from a newer Chevy.

[robotix]

The old engines are worse on gas, but you can help by adding fuel injection or if you can afford it, install a LS1 engine from a newer Chevy.

I'm talking taking something like a $5000 '68 Cougar with AT LEAST a straight body, and having anywhere from 10-15k to work with. Would there be more efficient engine/transmission combinations from Ford (just to keep it brand-equivalent to reduce the number of heart attacks from site-seers) that would do well here? (Keep in mind the 10-15 is for everything from interior, to paint, to brakes and suspension, etc)

But is a new motor and transmission the only way to go other than a fuel-injection conversion?