John K Jordan
What a job. I've installed a LOT of doors and I don't enjoy it too much!
I've cut down off-the-rack big-box doors when the clients budget required it and they are all junk. Spent hours cutting and gluing new wood inside hollow interior doors where the trimming exposed the inside or made the solid wood too thin. Horrible stuff.
In your case with the non-standard sizes I would be strongly tempted to rip out the frames and trim the wall studs if needed to slide in a standard size prehung door. That way the next time the door needed to be replaced it would be a trivial job.
When I replaced all the doors in my last house it was easier for me and a better result to rip out all the frames and start with the bare walls. I milled red oak and built new frames from scratch, installed the doors, installed custom-built oak doors, then milled oak for all the baseboard and window frames/sills. I liked the way it looked.
(I used to have more energy! )
I'm real particular about my doors. When we sold that house the guy told me later that what convinced him to buy that house over others was the doors. He said he was impressed by the effortless "snick" when they closed, every one, and with no slop!