Tail Shaft

Hi all, I am currently hotrodding a 1986 El Camino. The 2004r tranny i have is shot and I am looking at a th350 with about 25,000 miles on it since a rebuild. First, does anyone know the market value of a used th350? Second, the guy i am getting it from is getting a 700r4 for his 95 Impala, and he needs the tail shaft off the 350 for on the 700 so it will fit. Will it be possible to use the tail shaft off he 700 on the 350? One more question, what are the overall lenghts of GM trannys, or a source to learn.

Go here for info:

http://www.tciauto.com/tech_info/trans_dims.htm

thanks for the link troy and i hadnt thought about the crossmember, but it looks like if i go find a 6in tail shaft for a th350 at the junkyard then i will be set for lenght, seeing as the 200r and 350 (with 6 in tailshaft) are both 27 and 11/16 in. I'm not sure about the crossmemeber locations though

edit,it looks like i am going to have to move the crossmemeber regardless, towards the front about 7in.