BBC piston to valve clearance

[C101971]

Tried some digging but didn't quite find the answers I am looking for. I have a mk4 454 2 bolt main, bottom end is factory, running iron closed chamber large oval port marine heads, 1.7 roller rockers torker 2 intake, sniper efi. 3k stall powerglide, 4.11 gears with 28 inch tires. I am planning for a hyd roller cam.

With my setup listed above for reference, keep in mind my motor is disassembled except the crank, rods, pistons are still in it, I plan on keeping the bottom end stock. What I want to know is how much space does the valve have before it breaches safe clearances? I will not be running stock springs. I read lots about .550 before coil bind but I am building my heads, not pushing factory limits. I just want to figure out what measurements I have to work with so I can narrow down my options. I can't test for compression cause the motor is not assembled and I am aware that contributes to cam selection. I plan on keeping it N/A, and will be using factory thickness head gaskets, my block has not been decked and my heads are brand new.

Or if people could tell me about their similar setups and what your clearances were for stock bottom end w/ iron heads