1966 396 oil plug

[jb66ss396]

Can anyone tell whay marking should be on a '66 chevelle 396 oil pan plug??

[shadowgray396]

I have seen a "TR" or a "A" markings before on 66. They should be a 7/8 hex bolt. I have heard of many head marks that are know and accepted. My friends 66 Corvette has the 'A" mark on his.