I have a 66 C4 from a 6 cyl. car with neutral safety switch and kickdown cable for sale, if you need a rebuildable unit. The bellhousing is for a six, but I believe that the C4 is the same for the 6 as the 8. Others may know better, if so I stand corrected. Asking $125 OBO.
There should be a ton of Mustang owners out there that would be willing to trade a C-4 Auto setup for your existing 4-Speed and all of the related components. I would rebuild the C-4 in any case. They are relatively cheap to do (about $450 to $650). I think the C-4 is a great tranny and ran one 180,000 miles with no problems, then rebuilt it just because it was old. Let someone else worry about clutch discs, throwout bearing etc. I think autos are great and especially if it is a real daily driver. Good luck.
65 Conv., 65 & 66 Coupes and the remains of
a 66' Coupe with 6 cyl. engine and V-8 3 spd.
I'm one of the owners who would be interested in trading my auto set up for the 4-spd for my 1966 GT convertible. Mine originally came with the 4-spd but the PO did the swap because his disability prevented him from driving a manual. I've been thinking the same question as to cost of putting it back to the original 4-spd set up.