Make sure its the 88 or newer case(4L60), pull the pan off it and you should see one large valve body in the front and a smaller one in the rear. The older 700's were bad about eating rear planetarys, the newer case design has a secondary valve body just for the rear planetary. If you are going the overdrive route make sure you get the later valve body, much better transmission to build if you choose to do so in the future! You will want to add a transmission cooler unless you have one already...
http://en.wikipedia.org/wiki/Turbo-Hydramatic
The original version of the transmission had a 27-spline input shaft which was a common failure point. In 1984, 700R4's designed for use behind Chevrolet small block V8's received a 32-spline input shaft similar to those found on classic TH400 transmissions and which also used a different torque converter than its 2.8 V6 and 2.2 L4 powerplants. Between 1984-1987, internal components, from the ring gear to the oil pump housing, were updated, ending with the auxiliary valve body (for 700s manufactured after October 1986).
