is that tranny and t-case 200 each or together?
hopefully each, as i know the average auto tranny is close to 200 with a converter full of fluid, and i would put a t- case close to 100 lbs by itself, though i have never seen an atlas to know how much it would weigh.
and assuming you have an all iron SBC 400, you are about 200 lbs light on it as well.
just for reference, weights of different motors
http://www.team.net/sol/tech/engine.html