I have successfully run Crower 86050S Short Poly Locks with 1.50 Roller Rockers under stock Z/28 covers on more than one occasion. For added clearance, I've also added thicker cork gaskets such as the ones from Summit, or have doubled up with a set of regular cork gaskets and glued them together. Lots of clearance then but you can often get away with just the short poly locks noted above.
If you end up picking a roller cam that doesn't need as much spring, you could likely run a set of stock long slot rockers and use the regular lock nuts. I simply use roller rockers and screw-in studs as a performance preference, as well as added insurance against pulling a stud and maybe dropping a valve. There are plenty of reasons to upgrade the stock valve train on 186 heads when one has the chance. Especially when buzzing these things up to and/or over 6500 rpm as they were intended.
This one has roller rockers and poly locks with stock valve covers. If you look to the right side, you can see the thicker gaskets under those covers. (most people would have no idea it's rollerized, but I know, and that's all that matters)
