HI Scott
you need to make a tool to check the rockers, as thay are not all the same and swapping the rockers round could/will change the clearance, I made up this to check the rockers and had spare ones for adjustment,
I used a old rocker shaft for location and as you can see, if you fit the rocker on and adjust the screw to touch, you can then check the other rockers for gap or no gap, other wise you spend your time fitting rockers and shims to get the right combination for the valve clearance, some times the shims will not give the correct clearance , so checking and swapping rockers round could be of advantage
the last time I checked the shim part No's thay came back as N/L/A from Porsche, looks like you may have to try Henry's route and fine some Alfa ones or Andial or a race/engine builder that looks after 935's or RSR,s, the other option is to make some thick ones and grind to fit?? do not for get to harden them when finished.
regards mike