[Dragsinger]

How do you simulate head gasket thickness for mock-up and measuring when you do not have a gasket of the estimated thickness?

Easy, stack valve spring shims on a few head studs. In this case .030" shims showed me what I needed to know. [I need an .028" gasket]

Also, notice my doubled up checking springs. I have learned that in some situations the single checking spring does not have enough tension. If a valve seal is slightly snug or a valve stem has a heavy coat of thick assembly lube the checking spring may not follow the cam leading to inaccurate measurements.

The double springs assure your measurements are consistent. If you have ever had the experience of degreeing a cam and the results keep slightly changing this double spring tip may help.