if you haven't seen this article already maybe it can answer some of your questions, I know you are not dropping in a V8 but in order for them to do so they had to convert to a 5 lug
1964-1966 Mustang In-Line Six V8 Swap
Convert That Six-Cylinder Mustang To V-8 Status
From the April, 2009 issue of Mustang & Fords
By Wayne Cook
Photography by Wayne Cook
1964-1966 Mustang In-Line Six V8 Swap - Mustang & Fords Magazine
allow me to regurgitate a few highlights:
A V-8 conversion starts at the
suspension. These V-8-type spindles should be installed as a first step on any V-8 conversion. Don't try and get away with using the smaller six-cylinder spindles with the V-8 engine. It's not worth the risk.
Although the
control arms are the same for both six-cylinder and eight-cylinder cars, the coil springs are different. Replace the whole front
suspension with new hardware.
Five-lug wheels are needed for the V-8
suspension; as long as the five-lug conversion is needed why not convert to disc brakes in the process? The whole kit will bolt right onto the stock V-8 spindles, and you'll be adding a great deal to the operational safety of your car. You can buy this complete and excellent kit from
Stainless Steel Brakes.
not sure if you have to toy with the steering, or keep your existing one