Short shaft 400. You can either go to your local gm dealer or gm supplier and buy a new crossmember for a 69 bbc/th400 camaro, believe it or not, they still have them, and it should be under a hundred bucks. I will say that when I bought my factory th400 gm crossmember, the mount was welded about @one inch to the pass side of center, so the trans was not straight in the tunnel. I cut it off and moved it to the center, I think all factory camaro/nova bbc cars, the engine was moved a inch to the pass side for exhaust manifold clearance with the steering box, but I centered mine when going from a sbc to a bbc, so I had to move the trans mount. You can also do a search on here and there was somone making them out of chrome-moly tubing, which would be lighter and probably give you some more exhaust room, not that 4" should fit without a problem. For the driveshaft, I have used the original 350 driveshaft and found a old small cross section th400 yoke and it worked fine. You could also use a 1350 cross section yoke and just go down to you local parts house and find a conversion u-joint. Either one will get you going, but if you are making any serious power or the car hooks good, I would be heading down and just get a new driveshaft made with all 1350 series u-joints on both ends and some good quality yokes to match, it would probably be cheaper in the long run.