MYTF wrote:
As far as the 3 deg. angle if I remember correctly this was the best he could get what you want is 0 deg. between the output of the transmission and the differential. So if your transmission output is at say 5 deg. you want your differential to be at 5 deg. This balances out the small speed differences from the U-joints.
0 degree is theoretical perfect but......can cause u joints to fail over the long term believe it or not. for example 65-6 mustangs as they have aged tend to sack out the rear springs as i'm sure everyone has noticed. this leads to a very shallow ujoint angle particularly in the rear joint. under use the needle bearings never have a rotational force applied to them(due to no included angle in the ujoints operating cycle) so they sit in one spot resulting in dry spots and wear points due to loads being placed in the same spot all the time. now if the plane of both u joints are at 0 degrees and the u joints are offset even a little in some direction this problem goes away. in other words put the trans output 1 inch above or below (or to one side if you want to offset the motor for room and weight balance) the diff input and put them both at 90 degree vertical and no problems.