I'm looking at a diff with a small yolk. I need a big yolk, but this is a good deal. How difficult is it to change out a yolk? Does it bolt in or require more disassembly of the diff?

Why not do it the easy way and replace the U joint with a combo joint?

Sounds like a good alternative. Will the yolk size improve / decrease performance?

741 & 742 cases don't use a crush sleeve so swapping yokes is no problem, just remove the old one replace with new & torque the nut to 140+ ft-lbs... 489 has a crush sleeve & if you don't have experience it's easy to screw up so use the conversion U-joint...

you need a impact gun or a long pipe for leverage to loosen yoke.

As noted 741 & 742 case 8.75 rears use shims to set pinon bearing preload so changing yokes isn't a problem. My best recollection is that the torque spec is 225 ft.lbs. Pinon nut should be peened after torquing or locktited. 489 case 8.75 rears or any using a crush sleeve for pinon bearing preload is a tricky proposition and not advised. If you must do it, min. torque is 175 ft. lbs. When reinstalling I would go to at least 200 ft. lbs. Same deal on the pinon nut.

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Why not do it the easy way and replace the U joint with a combo joint?

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I did this and if you take your car far from home I would advise against it because:

Reason #2) The production of the adapter U-joint has greatly fallen off and therfore the price has risen sharply on these U-joints and they are incerasingly harder to find. I was told this by a rep for Mancini Racing.

reason #1) [and more importantly] My adapter U-joint failed 500 miles from home. I had a devil of a time getting another one. If it were a regular U-joint I would have been able to walk into any auto parts store and buy one but because it was the adapter U-joint the auto parts stores I went to could not even figure out how to look it up.

Bottom line for me is I decided to fix it right. I was going to change the yoke but decided to change the gear ratio too so I changed the whole carrier. This solved two problems and if I never tear up a U-joint again I know I just have to get to a local auto parts store to pick up another one.

Might be easier/cheaper to change the driveshaft end, no?
Or, if you buy a conversion joint, buy a spare.

Yoke means something that ties separate things together, as in oxen; the term pre-dates the car by hundreds if not thousands of years. That's why it's spelled that way.

Normally, when removing a 489 yoke for a seal replacement, etc. one can simply mark the relationship of the pinion threads with the nut so that the nut can be tightened to its original position thus retaining the original bearing preload.

But the replacement yoke might have a different dimension from the nut/washer surface to the rear of the yoke so the pinion/nut marking doesn't guarantee the same preload; but I'd wager that the dimension difference, if any, is so slight as to be negligible. I'd just mark the pinion thread and nut with a center punch, change the yoke and tighten the nut to that mark with some red Loctite.