I think the C5 had a early version of the lockup convertor. Throw that away.

Frank/Rebop

Bristol, In ( by Elkhart) 

Ditto on the C5 case.  My own tranny guy likes using the C4 guts (innards for you Texans out there) within that particular case.  The other consideration on a C4 is whether the transmission is a ‘pan fill’ or ‘case fill’.  My own druthers are for the case fill only from the leakage standpoint.  But my transmission guy does prefer the pan fill versions but only from a performance standpoint where the pan fill case is potentially stronger without the case fill hole in it.  Unless you’re running big horsepower numbers, it’s nothing to get overly concerned about.

Lorena, Texas (South of Waco)

If all you're going to do is cruise, then have him do a stock rebuild and maybe a shift kit. Almost any year would be fine, look for one the same length as your Fordo, or slightly longer if you can find one. That way you won't have to have a new driveshaft built, you'll be able to shorten the old one.

Frank/Rebop

Bristol, In ( by Elkhart) 

I am about ready to install a C4 in my bird. Do any of you Y Guys recommend any particular year due to reliability ,ease of installation etc.I have ordered my adapter from Mummert and am waiting delivery. So, I guess I need to go looking for one. There is a transmission shop about an hour away that rebuilds C4s for street/strip applications. I can get one there fairly inexpensive but I am interested in cruising not the 1/4 mile. Any thoughts appreciated.

55Birdman  Hickory NC