I wasn't aware the 29-3 was offered in a 6.5", do you have one?
That barrel length was supposedly discontinued in 1979...replaced by the 6".
My son has one of each, but he likes the fit and finish of his -2 a little better..the -3 is a 6".
The 29-3E and the -4 have the new style yoke retention (yoke screw has the little ball that runs in the V of the new style yoke) engineering change. I've peened a few yoke buttons over the years getting the yoke endshake out. That's a good improvement since the yoke screw no longer rides on the inside of the yoke button and also eliminates the wear caused by idiots that insist on swapping screws without fitting them to the yoke