Picked up a 1972 Ventura (ok, Nova really) rearend to swap in. Do I need to change the yolk or driveshaft length?

yes and yes. The driveshaft will be shortened about a 1 1/2

driveshaft length about 1 1/2 and install a different u-joint. The yoke will be ok. Don't remove the yoke from either rear end. They are not interchangable because one has more splines than the other, and it will also screw up the pinion depth.

I did this swap 2 years ago. My conversion went flawlessly.

I hired a welder to do the modifications to the perches. He set up a table jig to mount the old rear end, and then used my new perches that I bought, to align on the table to weld in to the new 8.5 rear. Mine was out of a 1973 Nova. The new rearend fit perfectly when I installed it.

I installed a new driveshaft rather than try to cut and rebalance an old one. My new driveshaft with new yolk cost me $185 bucks, balanced. It was better than my alternative. The old driveshaft was out of balance, and he could easily had that much cost into trying to balance and straighten the old one.

I used a string to measure the distance when the car is planted on the ground from end to end. The driveshaft guy told me how to do this. Then he made one to exact size and it fit perfectly.

I bought all new leafs, and shocks while I was down there.

I thought the later novas bolted directly in. I still have to mofidy the spring perches?

Mike, I did the swap, and you do not have to change the perches. I think 4dabird's did it on his 69, which may be different. I have a 68, and had no issues. I used the posi unit out of an 80 Camaro, and the rear out of an early 70's Nova (can't remember the year).

All 1st gen Firebird's have the same basic dimensions for rear end applications 67-69. On a Nova rear end(same as first gen Camaro), it's just the drive shaft that you alter. The spring perches are the same as first gen Firebird. On a 2nd gen(Firebird or Camaro) rear end it's both, the driveshaft and the perches that get altered.

Supposedly mine is a 73 Nova, and the parts work that way for bearings and seals. But I did have to modify the perches by about 3/4-1 inch. Maybe it's a 73 camaro and seals/bearings are the same? I am going by what a mechanic told me?

All parts that I have installed with end seals and bearings fit based on 73 Nova, but again my perches needed to change.

If you don't need to change it, all the better.

Right. If it measures right then you are good to go.

Either your mechanic hosed you for some fabrication work (fabricting a story about needing fabrication work) or the rear came out of a second generation f-body.

I lined both rear ends up and the perches did need to be moved. So it cannot be from a Nova.