I've only got experience with the C4 to AOD, but I will try to help.
There is a special AOD cross member (for the rear of the trans). This has to be bought, or built.
I don't know if you can drill/cut a 4 speed cross member. But judging from the shape of the AOD one, I doubt it.
You can check out this page:
http://forums.vintage-mustang.com/forums/showflat.php?Cat=0&Board=forum&Number=558985
Since you don't have an auto shifter, you'll have to get one.
I've been curious about whether or not the shifter (cable) from a tbird (or I guess a mustang, I have a tbird parts car) would work in a mustang. You'd have to put a console around it, or something to hide the "parts" at the base of the tbird shifter. I'm talking about like a 93 tbird or something. Just food for thought, but you have to get a shifter. Maybe a 60's mustang auto shifter is the easiest course, but you have to buy/build the shifting rod. (see the other link , it has the part listed)
I'd read up on it more, then see if your guy is willing to fork out the $$$. Its not free, for sure.
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