I have a crate engine in my 81.  Let me say that I HATE chrome.  OK, I love the look most of the time except when it's dirty which seems to be 5 seconds after I clean it.  The valve covers on my car are center bolt generic chrome and cheap.  I was looking to replace them with a set of finned valve covers from a mid year.  Drill holes, have spacers welded...I used to work in a metal fab shop with some great welders(of which I am not one).  I then decided it would be a most unholy act to desecrate those covers and ended up selling them to a local for his restoration project.  

You can buy adapters so you can use standard perimeter bolt small block valve covers on a center bolt cylinder head. I use them on a crate engine in one of my cars. They work fine. There's a huge number of small block valve covers out there to pick from. The adapters are available from GM Performance, Trick Flow and I believe Jeg's sells their own brand adapter.

http://sdparts.com/details/gm-performance-parts/24502540
I tried them out on my crate engine. They worked out ok.

Summit or one of those other parts places may have them cheaper.

They make adapters to bolt on to your center bolt heads that will allow you to use the early, perimeter style valve covers....then you could use any older style covers you wanted, including the finned "Corvette" script ones. HERE'S one example just to show that they exist, and how they work. There are cheaper ones out there, tho.

Those look perfect.  I think I'll contact one of my buddies who works at a machine shop and challenge him.  "I bet you can't make something as nice as these fir a case of beer"

If for some reason your buddy cant make them, I will be selling mine.

I'm yanking the crate engine out of my vette next week to make way for the LS1 swap. The engine is being sold with the chrome OEM center bolt valve covers to a local guy.

Dave I bought a $5 can of black wrinkle and made the chrome go away!............ebo