Can anyone tell me the difference between the stock GM cast aluminum valve covers that come on the Gen VI 454/502 engines and the HP500 Merc covers? Is there any difference other than the logo and pretty paint? I have a good set of the stock covers and I was hoping to run them with a set of Comp Cams aluminum bodied full roller rockers. Cam will have about .570 lift. These covers do not have drippers on the underside.

I doubt there is any difference. Paint it blue and triple the price.

Merc grinds off the drippers on them. Other than that, they're the same thing with $500 paint.
10 minutes with a Dremmel & you can take care of the drippers too.

For whatever reason, mine did not appear to come with drippers, if I remember correctly. I'll have to pull them out and look at them again. Time to get the blue paint out!

I bought two brand new Gen VI engines and roller rockers would not fit under the stock valve covers.

Hmmm, do you recall if they had the drippers on them? I have read that the main point of contact is with the adjusting nuts and set screws (polylocks). I might try to see if I can run an extra thick gasket with them.

I was running a set of aluminum covers on my 454 that looked just like the covers that Merc put on the old 420's. These just barely cleared, but they did not have baffles for the breathers or oil fill cap. As a result, I had issues with oil seeping out around the grommets.

I have a pair of factory ones that came with no drippers..non HP500

I have a Gen VI block that I have HP500 heads on and we are using the stock valve covers with the drippers grinded down. No clearance problems.

Mine had no drippers either. These are the stock cast composite valve covers. Valve train is not adjustable.

Don't these valve cover use molded o-rings? I have seen two different versions, the only external difference being the location of the oil fill hole.

You can bling them up yourself with some scrap pieces of stainless steel laminate and some double-sided tape...