I just went from a th-400 and went to the 700-r4 and have no regrets at all.........You can use the stock crossmember as lond as you get a tail shaft from a late 80's Caprice, caddy or buick roadmaster 700-r4...... Here is a link to that :http://www.chevyhiperformance.com/techarticles/46278_automatic_transmission_overdrive_install/index.html. YOu will need geometry corrector brackets and a TV cable bracket as well...............Available from Jegs or Summit........Both the 200 and 700 are great tranny's if built right.......I was able to throw 4.10 gears in my car and still cruise the expressways at a low rpm
As far as the driveshaft.....you will need 49.5" from center of U-Joing to center of U-Joint--that's with a 7.5 rear or 12 bolt.......and take off another inch if your going to the 8.5 rear. Hope this helps...
1984 Monte Carlo with sbc 388 stroker ( dynoed 514hp) 700-r4 , 12 Bolt w/4:10
Old Chevy's Don't Die, They just get faster!
Best ET to date : 12.20 @110 Mph All Motor