Standard bore on the Chief is 2.375" (two and three-eights inch). Year of manufacture and whether its a racing model or fishing motor doesn’t matter, they used the same size bore. Racing model reportedly built with two-ring pistons and aluminum rods as standard equipment. (usually changed over to bronze). Personally I’ve never seen a two-ring piston in a Racing Chief, but have been told they exist.
Your bores should measure at least 2.435" if the slugs are indeed 6o thou oversize.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...