slip yolk length

I saw a few 904 yokes for sale with different lengths...I got a driveshaft that is about 1.5 too short officially and the tailshaft needs to stick out about 2" to reach the U-joint. Can I use a longer tailshaft to correct this? Im planning to space the rear axle another .5 back due to some larger tires so Ill really be out 2.5 after that. Just trying to reuse this driveshaft if at all possible. I got no specs on whats in there at the moment to compare the lengths but why do they make the 904 yokes different lengths anyway?