The 9 inch tailshaft length TH350 should fit in place of the 700r4. There is room in the yoke play for the difference in trans length. You will probably have to slot the trans crossmember mounting holes or re drill them because of the different trans mount locations.
Is he going to have to buy a TH350? If so I'd rebuild the 700r4 they can be built more then strong enough for a stock 454 and you'd still retain the overdrive which is really nice for long highway runs with gas prices the way they are.
Heck if I was close to you I'd give your friend a TH350 for his 700r4. I've got 3 backups and I'd like to have a 7004 to rebuild.