how critical is installed valve spring height?

[68-500]

I haven’t read 1 thing about a spring alignment shim on the bottom of the spring between the head. With out it will the spring not eat its way down into the spring pocket? Well let me slightly rephrase. It had what you called shims under the spring. But you talked about removing them to get spring height. Did you end up with something in between the spring and pocket?

 

[451Mopar]

I haven’t read 1 thing about a spring alignment shim on the bottom of the spring between the head. With out it will the spring not eat its way down into the spring pocket? Well let me slightly rephrase. It had what you called shims under the spring. But you talked about removing them to get spring height. Did you end up with something in between the spring and pocket?

I am thinking the machine shop might have put shims under the spring seat/cup locators that prevents the springs from digging into the aluminum head.
Usually the spring cup / locator us 0.060" thick, but I got some 0.030" spring locators from PAC. They look like they just machined 0.030" off the bottom of the 0.060" locators.
Are you using the Hughes valve springs or the 440 Source valve springs?