I will give you my opinion, but you have to decide what to do for yourself.
A 66 coupe will need to have the shock towers removed in order to fit the engine. This means a rack and pinion front end with a mustang 2 type suspension or some other front suspension that will totally replace the shock towers.
If you are handy-you could maybe do this for 3 grand- if you are not an accomplished welder fabricator, someone is going to sell you a kit for 3K plus and then you can pay for the installation.
You will need to rewire the car, add chassis stiffness with bracing or subframe connectors or both, with the added power and will likely need to upgrade the braking system all around.
It is a huge undertaking to do it right with lots of unmentioned expenses
AND you are doing it to a coupe which will not have a sufficient resale value to cover more than a fraction of your expenses.
Now in a fastback, it might make financial sense, but even then, I'd shy away from a mod that significant.
