I admire the jukyard-budget intent, and have been running Toyota joints and shafts between Isuzu yokes since the mid-90's, but even so, you've still gotta shorten/lengthen the donor driveshaft to fit your Isuzu, right?

BTW, I like Matt's adaptor from a design-elegance perspective, and the alignment puck like RobG uses for simplicity's sake -- but the path of least resistance, IMHO, is to take 15-20 thousandths off the inside of each side of the Toyota yoke and just run the Isuzu joints and Isuzu flange-yokes.

I know this is a bit off-topic, but is an example of a requested product for which market definitely exists, where the market is at least partially-served by several work-arounds. Thus this request ends up further down in the list of priorities, for most manufacturers, who seek a market where clear demand exists without much competition (either with a workaround or with other vendors).

FWIW1: all bets are off if you have 1310-series joints... but then again, you have more choices on that side, as well. IIRC, there's a 1310-to-Toyota conversion cross available, tho, so you might be able to leverage the 'Zu/Toy similarity.
FWIW2: you can run a TH200 slip-joint from a late-70's Caddy luxo-barge in place of your Isuzu slip-yoke at the back of the transfer case and use the Caddy CV on the Caddy female-splined slip to mate to the Isuzu male-splined shaft and slip seal.

Options abound.

Randii