I helped another member (DabeastII) hear install the gear vender on his 727 for his 512 69 super bee went on cool as heck. think he had to make a couple small dints in the tunnel nothing much.
On changing the output shaft no and yes no because the standard goes right on just by changing the tail stock
But there is a version that uses a shorter output shaft too where you change the output shaft and come out with a shorter version!
They have them for every aplication.
http://www.gearvendors.com/appguide.htmltell you the 69 bee with 3.55 dana in OD cruising 80 mph at 2300 rpm is cool!
