Is there a way to check valve to piston clearance with heads on. Changing to a bigger cam. Trying to use what I have.

Yes, pull a pair of valve springs on cyl #1 with an on head valve spring compressor & sub in a pair of light checking springs. with some 3/8 white nylon rope in the cyl to keep from dropping a valve & then check the VP you have now for a start. there is a range of crank degrees (each different) where the 2 respective valves are the closest to the piston. Others will chime in.

Run the piston up to TDC on the exhaust stroke, remove the valve cover and use a pry bar on the rocker arm to push the valve down against the piston...use a dial indicator to check the valve's travel.

You need to check with the checking springs as mentioned usually from 15 before TDC through 15 after TDC. If using a cam with the same lobes intake/exhaust, and the cam is installed straight up, the valve distance will be the same at TDC from the head seat. Clearance may be slightly different because the valve reliefs may be different depth, and because the valves open at an angle, the larger diameter intake valve should have less clearance.
Advancing and retarding the camshaft installed position will change the P-V clearance, Advancing will close the exhaust sooner and open the intake sooner, so in an advanced install position, the intake should have less clearance (given the same cam lobes, but usually the exhaust is larger duration.)

Check intake at 14°, 12°, 10° and 8° btdc, and exhaust at the same numbers atdc, at overlap.

I have seen someone put feeler gauges stacked like checking lash and turned the engine by hand to check v to p

Thank you all.

I would try the stacked feeler gauge method. I'd clamp em in the middle or somewhere other than the normal tips so when done you can still use em normally cuz the tips will still be pristine.

Assuming you are talking solid and not hydraulic lifters, the rules depending upon approach may be different.

this is how ive done it,never had a prob.

Yes, with juice lifters, with a pair of junk lifters I lock the cups solid with JB weld/washers the same distance below the snap ring as the preload I will be using then use them for checking purposes.