Yeah it's to bad they discontinued those!

That's not bad, only 1/8" variance. Shims or a bigger hammer always worked on sheet rock. Cut your jambs 4 13/16, most trim will handle a 1/16 variance easily.

Use the widest measurement within the opening for your jamb width on all 3 sides. Casing should be fit to the jamb, you can fill at the wall where necessary. Shim and fill at the wall only where casing does not sit flush with the wall. That view is secondary to the front view of the cased opening.

You just have to make it work to get the best result along the front of the area which will be most visible.

When the sides are different sizes you have to see what will work best. Side pieces are usually cut the same width, in some cases the sheetrock can be dimpled, you can put in-fill pieces in the back of the outside casing against the wall, etc. Each situation is different and best solution is per case bases, just have to "finesse" everything to achieve seamless result where only you will now that something was off.

start with the wider width and use a block plane and chisel to dress the proud spots. Or get out the plaster tools and float the wall surface to the jambs like they used to do before drywall.