318 build up

I like rumbles train of though. That 400 h.p was with STOCK magnums. 450 is easily doable with porting.

If you use the mags stick with a single pattern cam. Shoot for 10.5:1 comp.

Magnums have a 1.6 rocker ratio. This will increase your cam lift. Retainer to guide interference becomes an issue around .525 lift. Hughes has springs and retainers that will get around this with no machine work.

Just remember that the more radical the engine gets,the less friendly it will be on the street. Issues with overheating,idle quality,plug fouling and little bottom end torque are some of what might happen. You will also need deep gears and a hi stall tc.

I would say keep the lift under .500,the duration under 235 and hit it with a 150 shot.