rjsfocus,
Exactly. Slide in your circular T square and rip 1" off the jamb legs and head - sand smooth.
Remember, cut the side of the jamb opposite the hinges and keeper.

If you have a table saw, its' even easier.
Custom size doors or jambs are rediculously priced and if you are capable of doing it yourself, do it.

All the best,

The PorchGuy

my sisters house had the same problem .the walls were hardcoated so 4-9/16" wasent enough..we used an adjustable door ..its a complete pre-hung .. think they came from a builder surplus...the jamb is split in 2 ... 1 piece sliding into the hinge side..they are adjustable from 3.5" to 4-7/8". if there not to pricey that will be the only interior doors i will ever use!!!ive used them before a long time ago but have no clue on the price now.. nothin is ever plumb and true so this gives u slack to play with...i ended up puting them in since she fired the contractor!!! but i will tell u 1 thing , she didnt fire him for buy'n pricey materials!!!!
hope it helps.. Scott

If you dont want to cut the jamb down, which is pretty difficult for even an experienced tradesperson w/o pullin the jamb apart, another avenue is to center the jamb in the opening. You will have about 1/2" sticking out each side. When you go to install the casing, get some 1/2" x 1/2 or 3/4" moulding to fill the void at the outside of the casing. If your casing is paint grade, fill and caulk at the sides where the 1/2" meets the casing w/ light sanding, you'll never see it and will only look like a heavier casing was used at the sides.

Yes sierraest that definitely another way to do it. FIll in behind the outside edge of the casings with parting strip 3/4 x 1/2.

GOod Luck

All the best,

The PorchGuy

Here is a link that might be useful: My Album

Awesome porch work, PorchGuy! Great album!