I have been staring at these open engines for months - shimming the spring does nothing more than add compression to the spring... making the closing pressure higher. There is nothing to adjust or shim for valve lash - it is what it is. A cam operates a hydraulic lifter that pushes a pushrod that hits a rocker arm that opens a valve. It all just works for valve lash, unless you bend a rod, collapse a lifter, wear a cam lobe, have a loose rocker arm hold-down bolt, etc....

If you want faster spring action or more valve closing strength, go ahead and shim. When I pulled my springs, I also replaced the valve stem seals.

Oh sure Tug... introduce yet more expense.

 

It's only money.....