I have a little problem, the 67 stang i bought the 3 speed is wasted, i have axcess to a 4 speed out of a different mustang to use until my t5z is built, what would need to be changed to put in the 4 speed if anything ?

 

What engine do you have in there?

 

351 w but it still has the stock 289/ 3 speed bell housing

 

Since you need to replace the trashed 3 speed manual anyway, drop it on the floor along with the bell housing and get that 4 speed top loader onto that bell housing if you can. Not sure about the bolt pattern and the number of bolts. What you need to confirm is... bolt patern...box to bellhousing, then input shaft length, face of box to end of input shaft. The input shaft spline should be the same, but also needs to be confrimed.
As far asI am aware, the 3 speed and 4 speed toploaders share the same housing/clutch splines. You should already have a 10" clutch, so you should be good to go there.