Driveshaft question:

You will not have any length issues when going from 7260 to 7290 joints.
When I had a drive line cut for my car I went to pick&pull and got one out of a big block c body that already had the 7290 and just cut it down and trough new joints in it.
When they asked for the trans to rear measurement they had me measure 'car on ground' from the end of the output shaft to the flat of the rear end yolk, works great.