First of all, Thanks for reading and replying to my problem,
The Main shaft is the one that comes out of the back of the transmission and I always called it the output shaft. I looked up my 1956 copy of Hot Rod magazine that had an article on Lincoln transmissions to check on the correct name for the shaft.
On the back of the case is the rear engine mount that bolts onto the case with 6, 5/16 or 3/8 bolts. The spacing across the transmission is 3.67" from center to center of the holes. This mount is for a closed drive line. The 4.25" is the spacing for the 6 bolts that hold the rear mount on the Ford 4 speed transmission. This mount is for an open drive line. At first glance they looked like they the same except that one was for an open drive line and the other was for a closed drive line. but when I took the mount off of the 4 speed and tried to put it on the Lincoln, it wouldn't fit. The 8" refers to the spacing of the holes for the bolts to attach the mount to the cross member.
My Pickup came with a 4 speed transmission. It had a flathead 6 cylinder engine. The main shaft on the original transmission is 6 spline and it measures 1.31" in diameter, whereas the Lincoln is 6 spline but measures 1.19" in diameter. ... I looked at the original message and there is a mistake in the numbers. Should have been 1.19" and not 1.91". Sorry about that! I didn't check the shaft sizes either, until the other problems developed.
A friend of mine gave me a yoke that fits and will also take the speedometer drive gear so now what I need is the rear mount that is for an open drive line that has 6 holes that are 3.67" from center to center measured across at the widest point. How'ed I do this time?
Thanks again for any light you might shine,