Yeah, see he's says "im selling them complete with ford motorsport 1.6 roller rockers they are shimmed for a decked block". Then says in the questions:
"Q : what exactely do you mean shimmed?"
"A: the shimms are for valve adjustment for a decked block to run them on a stock block you can remove them easily"

The rockers are shimmed because if you put the head closer to the block with the same size pushrod, it will push on the rocker and unseat the valve a little. Probably lose all your compression...Take them out on a stock block and they're fine.

 

i heard of shimming a girl before ,so you wouldn't fall in...[&:]same as 2x4 i think ...