[Cathair]

you can get a kit to do it...

Modern Driveline - 5 speed Transmission Swap - T5 and TREMEC TKO ...
Modern DriveLine is about five speed transmission repairs and conversions. We offer complete easy to install T5 conversion kits for early model swaps in Mustangs, ...
http://www.moderndriveline.com/Technical_Bits/classic_swaps.htm

 

[jonni]

Clutch, pressure plate, throwout bearing, flywheel, bellhousing, shifter, clutch peddle, driveshaft, and trans crossmember.

 

[llevelys]

bellhousing adapter,
modify transmission cross member,
shorten drive shaft