im replacing a 318 small block la engine with an ATK 408 cu in magnum engine and my old engine mount brackets are not exactly usable. is there anything on the market that will
There should be ears on the Magnum motor like your 318. The passenger side is the same. It's the driver's side that's a little different. 340/360s used a different driver's side mount.
The passenger side bracket will work as is. The 318 driver’s side is 1/2 or 7/16 inch wider than the 360 Magnum mount but can be used with a spacer, or a couple of washers, etc.