The 92-93 manifolds had the 2 1/8 outlets compared to the later 1 7/8 outlets. If desired, look for 92/93 and extremely early 94 model vehicles. Theoretically they flow better, but the gain will be negligible in a daily driver. Car Craft and Dulcich did a dyno test of the exhaust options on a 360 years ago and the difference between log manifolds and 340 manifolds was not that impressive at most rpm. Magnum manifolds are about the same (maybe better ?) than 68-70 340 manifolds.

The other difference is that the 92-95 passenger side manifolds were drilled for EGR while the later manifolds were not.

They also like to crack just before the middle cylinder outlets, toward the front, in that neck area.