Valve / Piston Clearance in 383

That looks at least like .100". Remember, it's not how much the valve opens, but when. The duration has tons more to do with piston to valve clearance than lift because as the piston is coming up, the valve is closing. It's going to have to be something that needs to be measured for sure. Damned if I wouldn't cut reliefs in those pistons if that's what it takes to run more cam......but I doubt you will need them.