Need 4 speed advice

Here's what you are going to need:
flywheel
clutch
bellhousing
A body transmission
64-66 pedals and clutch linkage
64-66 4 speed floor hump
Your automatic transmission crossmember and mount will work, and if you get a 64-65 4 speed you can use your driveshaft. 4 speeds and 904 autos are the same length. If you want to lose the ball and trunnion driveline, get a 66 up 4 speed and have a driveshaft made up with a 727 front yoke. The floor hump is needed to have room for the shift rods and shifter. Brewer's has a fiberglass repop or you can try to find an original. 67 up floor humps can be made to work but it's a toss up whether it would be easier to make one or modify what you get. The repops I've seen have been for a 76 A body although they are listed as 67-76. All you really have to do is swap trannys and pedals. Hope this helps.