Help with engine serial number
 

Can someone check out B461496 for me? This is the number on one of the valve covers, I couldn't find a tag above the starter. It should be a late 80s 260 5.7l. There isn't any other letters or number before the B. Pretty much just need the specific year of manf. but a service history would be nice, too. Thanks

ps - I've already checked mercurypartsexpress.com and they don't seem to have any inormation on it.