Hi Hoss
Well, as for the steering, I don know...
But one source is, NPD (national parts depot),
for the AC system.
They have it for
65-66 6 cyl
65-66 8 cyl
same price, jus a few diff parts I think, the price is $895.00
They have those in
R 12 R134a
They say there isnt a fan shroud in the 65-66 6 cyl cause the 6 blade fan eliminates the need, um whaever.
It specifically states in the ad
"This system can be installed in cars that never had AC or cars that had it at one time."
As for changing engines, I think I still have a pair of engine brackets (these r what u attach to the beam at the base of the shock tower.) for converting from 6 cyl to V8, I bought em from them awhile back, never used em, the price in the book is $124.00 They fit 65-70 all sb V8s, big blocks must drill xtra hole.
The insualtors I bought were for a 351 windsor but I've decided to go w\ the lil 6 cyl so ... I don know which is closer, but the store # in the state where I live, toll free
1-800-368-6451 that ways u can call and inquire about all that, get a catalog etc...
U might could try Mustangs Unlimited, NPD and PAW, only thing is, PAW u have to buy their catalog, proly $5, but its over 1000 pages, it isnt Mustang specific parts, but there r some parts in there for it and jus about every other kind of vehicle...
Also dont forget about local parts stores for some things, like Advance, Autozone, NAPA etc, well for things like vavletrain, torque converters and other miscellaneous...