Thinking of switching from M1 single plane to LD340 but LD340 would need to be milled to fit. Is it worth it?

It really depends on the rest of your drivetrain setup, gearing, vehicle weight, and camshaft, but I honestly think the only thing the LD340 would do over an M1 single plane (which is an improved copy of a Holley Srip Dominator) on a 416 stroker is make the car go slower than what it is now, even with unported J heads...