Use the 90 T5 and go with a QuickTime bell RM-6053, it is bolt in, no need for pilot bearing spacers and it clocks the fork down low like a II bell for easy header clearance. Granted they are not cheap, but it's worth it. I also went with a Fox clutch and fly wheel (I have an 83GT engine in mine)
Buy Quick Time Bellhousing RM-6053 at JEGS: Quick Time Bellhousing Steel Bellhousing 1974-78 Ford Mustang II. Guaranteed lowest price!
www.jegs.com
Also, get a trans brace from Classic Auto Reproductions, you use a MII trans bushing.
1974 - 1978 Mustang II T5 Cross member. This T5 cross member will work with Mustang II V8 when using: 1985-1993 Ford V8 T5 Bell housing 1985-1993 Ford V8 T5 Transmission Bell Housing and works with the stock rubber mount
classicautoreproductions.com
If you want to stay with the MII clutch set up, Classic now carries them as well!
Specifically made for the Mustang II Stage 1: Street, Drag, Drift, Road Race, Rallye, Pulling, Autocross Features an integrally molded carbon Kevlar-based, high performance organic lining that offers smooth engagement and excellent life. This lining has an integrally bonded steel backing for...
classicautoreproductions.com