Looks
very much like a 230 or 250 to me.
Here's another of the same valve cover that "stock49" pointed out on Ebay that I just snagged for 14 bucks. Just needs to be stripped and repainted.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4500143323 These valve covers are on Ebay regularly and be had pretty cheap. They fit the Mercruiser 165 HP inline 6 engines (which is the 250 CI) and are usually marketed and sold on Ebay for Mercruiser engines.
They're made of aluminum, have a thick flange (like the Offenhauser) and (unlike the Offy) already has the PVC port cut into the top. I'm running one on my 292 now. Nice inexpensive alternative to the Offy (though I really like that polished finish).
-magic mike-
