bill wrote:
can i easily modify a new 2x4 prehung door jamb to fit my 2x3 framing?
or do i need to special order? thks bill

"Easily?" Not really. Prehung units are made to slip together at the
jamb and trimming there screws that up. It would be simple enough to
trim a 1/2" off each outer side of the frame except it's very difficult
to get the casing trim off w/ tearing it up. Unless I had a bunch of
them, I'd probably just opt to make the frame for it from scratch as
being quicker and simpler. But, I've a full shop--depends on what you
have to work with...

--