Check out this link for tranny I.D. - http://www.maliburacing.com/auto_tranny_id.htm

The headers might not fit unless they are for that body stlye. You will have to set the headers down in the body just before you set the eng on the frame mounts. As for the 700r you have to get a shop manuel or go to a auto parts store and look at the bolt pattern and the pan. The pan is different looking from the rest of the gm trany's. Or go on line and fine the trans and match it up