As Craig said, cork will work just fine. However, if you will be pulling a valve cover often for any reason, a rubber gasket with a steel skeleton is best. I reuse mine over and over and over. No scraping, no mess.
Back in the 60's when I was running solid lifters I used the cork gaskets. We would use Permatex #2 and seal the cork to the valve cover. Make sure surfaces are clean and put a light coating of grease on the head or gasket. You could then pull the valve covers to adjust the valves and the gasket would not stick.
This same discussion took place over on the Mustang forum. From my experience rubber with a steel core is the best material as it seals over and over again and does not lose its shape. I purchased my set back in 2011 for a 302/351W at Summit racing. As I said before I've removed the valve covers over and over and over again and the gaskets are still just like new. This is the second set I have ever owned, the previous set was sold with my former 357W engine. They are a Summit product part # SUM-G2321 if anyone is interested. Apparently they are only made for the most popular applications as I checked to see if they were available for your 200 six. I also checked on the web. They are not. Having said that, rubber is your second choice if you plan to remove your valve covers over time. I used to perform the same procedure as WADDN described however, Permatex #2 will eventually become hard due to engine heat and the cork will become hard and crack. If you want to maintain the original look of the engine cork is the correct choice. If you don't plan to remove the valve covers, you can choose either. If you do, rubber is the answer. Sorry If I raised your expectations!
The small block six Valve Cover gasket usually seals with cork or rubber with no problem but over time sloppy R&R can distort cover and some are just harder to seal period. Rubber and cork are available. A gasket sealant isn't necessarily needed BUT many use different means like the Permatex#2 for more confidence. I use cork and a gasket sticker like Hi-Tack or Copper spray to stick and seal it to the VC. The head should be flat enough, just get it dry and clean - like with a solvent wipe. RTV silicone ,( imho) is the worst possible $#^% to put on a gasket, making it slip out of place and contaminating your engine. Permatex #2 will definitely work and next time when you try to get it off - you'll remember this post... have fun
I replaced my valve cover gasket with the rubber gasket and it leaked. When back with the cork and no more problem. Tighten the cover bolts a little over finger tight or 3 to 5 ft lbs. or it will push the cork out and leak
I have a rubber gasket on mine...glued to the cover. I have solid lifters and do remove my cover a few times a year for adjusting the valve lash. I've had the same gasket for 4 years...never have a leak.
