They are not identical. There is more than one TH350 case. The main ones are the two wheel drive case, (minimal thickness on the bellhousing bolt holes), and the 4wd "K" case which has the thicker bellhousing tabs. There is also a fairly rare HD case (has HD stamped on it).
The 4WD "K" case is common and you can tell the difference by the thickness of the tabs where you bolt it to your engine. If they are thin, it's 2wd. "K" cases have a big "K" stamped on them.
A forum community dedicated to custom off-road vehicle owners and enthusiasts. Come join the discussion about trail reports, builds, performance, modifications, classifieds, troubleshooting, fabrication, drivetrain, and more!