Paul. Jim's info. is good. If you don't have the FoMoCo casting numbers / letters on the rocker arm rib between the adjuster and the valve stem contact, the rocker arms are aftermarket replacement units. There were numerous companies that made replacement units OR sold them as theirs. Because most y-blocks between '54 and '64 used 1.43:1 ratio rocker arms, that's what most replacement rockers are, 1.43:1 ratio. Back-in-the-day there were some companies that made 1:54:1 replacement rocker arms for replacement or performance purposes. My memory is getting dim, but Thomas was one name and (?) Gotha (maybe not quite right) was another. Hey, this stuff IS getting old, isn't it!
Per John Mummert's web site,
- '54 - '55 have EAN letters cast on the rocker arm rib and use a jam nut - 1.43:1 ratio
- '56 have ECG 6564 letters & numbers cast on the rocker arm rib and also use a jam nut - 1.54:1 ratio
- '57 also have ECG 6564 letters & numbers cast on the rocker arm rib, but use the self locking adjusting screw - 1.54:1 ratio
- '58 - '64 have 5751066 numbers cast on the rocker arm rib and use the self locking adjusting screw - 1.43:1 ratio
JM's got someone supplying him with new cast iron 1.54:1 ratio rocker arms. I saw them on eBay some months ago. I suspect that they're being produced in lot quantities. Perhaps John's supplier made more than JM ordered and then tried marketing them, too.
Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York