.557" purple shaft 318?

I think it will physically fit and work without piston to valve interference. Of course, you'll want to make sure of that......and really, the only way is to remove the heads and use clay to measure by. However, I think you'd be much better off with a different grind strictly from a power standpoint. I believe that cam will bleed off too much cylinder pressure and give nowhere near the results you're looking for. I think this would be a great choice for a step up in cam.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=640&sb=2

Those are Mopar specific lobes, not chebbie lobes. There's more area under the curve. It's essentially a revamped version of the 474 MP cam. I think it would work well for you.