Checking piston to valve clearance

What is the best way to check p/v clearance?86 flat top short block with E7 heads.I assume something must be done to make the lifter solid so they don't collapse and give you a false clearance.Also is it better to check with a head gasket or without and add in the thickness (compressed) of the gaskets I will be using?I see people talk of renting a piston notcng(flycutter),Where can you rent one??