That pic of the slip yoke in the rear of the trans looks to be the correct length...
you have approx one inch space on a 5 inch slip yoke length...
The rear seal on some of these transmissions came with a secondary seal boot that took up that space....
I am assuming the slip yoke is pushed all the way into the trans in the pic...
Pull it out about 3/4" when you measure your shaft length U joint center to center...
