Getting the most power out of my 400 stage 6 heads

I've had STG VI heads here that after having been worked are in the 90+cc range. 10cc's on a small chamber head is about .065". This reduces the P-to-V clearance the same amount.

If you have two cams with the same lift and duration but having different lobe separations, the one with the wider lobe separation will close the intake valve later and reduce cylinder pressure. Piston to valve clearance is measured during the overlap phase when the piston is close to TDC. Yes wider lobe separation is more forgiving on piston to valve clearance.

You want to have someone tell you what cam they ran in their engine and guess if that will work in yours. Okay.....I've run an old .600" lift solid roller, 280/280 @ .050" on a 105 degree lobe separation in a low compression 383 with 906 heads. However, I did measure the piston to valve clearance and cut valve reliefs in the stock cast pistons. Results? 525 HP.

So then it sounds like your plan is to measure nothing and hope another's cam will fit. I say put any cam in there you want to run and fire it up to see if anything bends. If nothing breaks you are good to go. Best of luck.