There have been some warnings about coil binding with certain aftermarket valve springs, so I thought I'd check.
The thickest feeler gauge I have is 0.032". At full lift that will fit between the coils, just barely.
My fitted outer spring length is 1.311", WSM spec is 1.37". However, I am using Black Diamond valves. To quote JH, "Note: The margin on Black Diamond valves are .020 in. thicker than factory valves. This can close up both the fitted valve spring length and the valve-to-piston clearance."
Should I be concerned? Maybe use a thicker head gasket?
Valve spring coil bind is always a concern with non stock parts. If the engine is assembled, a rough check is to lever the rocker with the valve full open to see if the valve will open more. Not that accurate unless you get in there with a dial indicator to measure but it will give you an idea.
If you just took the springs out of their wrappers, a drill press, and old valve and digital calipers can give you an accurate coil bind dimension. This photo gives the basic idea, just use a caliper instead of a ruler and omit the plastic scale.
Lastly, head gasket thickness has no effect on valve spring fitted length so don't worry about that, at least for this problem, but it will have an effect on valve to piston clearance.
To check that, use a blob of clay in your valve reliefs, rotate the engine 2 full revolutions and disassemble to find out if you have a valve to piston clearance problem. .060" to .080" is usually considered safe.