One difference is that the later M44 has extra emissions equipment the M42 didn't. There's an extra hole in the block-side flange where the exhaust check valve pipe connects. It looks like that started maybe in 01/97. There's a third part number that ran from 09/1996 to 01/1997. It's 11621432343. The only other obvious difference appears to be that the later parts have the bolts welded in to the cat-side flange. The earlier ones look to have separate bolts. | 
Header/Manifold question... 
Linear Mode
