With my 4l60 and np207c I am 42.5" from tranny bellhousing to TC tailstock. Another member here measured his th350 and np231 to be 42". I'm not sure how individual component lengths compare, but our total length is pretty similar.
To get a strong 700r4/4L60 you just have to get a "K" case. They are from the chevy 4x4 trucks, and literally have a large K on the side of the case. They are all post '87 (when the improvements happened) and I believe have some heavier duty stuff in em.
My rear drive shaft is actually stock, unmodified. The overall length of the driveline is pretty close to a 2.5+ax-5+np231j. My front drive shaft I shortened a bit, but now with a 4" lift its a hair short.
Also, install your motor high, this allows you to tilt it down to the transfer case, and gives you much reduced driveline angles. My motor is installed so it just fits under the hood, and with a 4" lift I have a better rear shaft angle than it did stock.
A 700r4 shouldn't cost you much (if any) extra over a th350. There's millions of them in junkyards in perfectly good operating condition.
1993 Jeep YJ - 350 Chevy TBI, SM465, NP241, 14B SF LSD, 10B