small block ductile iron adjustable rockers

Thanks Toolman! Yep, that's the ones. So my guess is the ones w/ the part number that begins w/ 24 are 1st year 273's. The ones w/ the W's, could they be for 340 t/a heads? or just a later 273 casting? Enquiring minds want to know........

I have a 66 HP 273 and as far as I can tell it has the original rockers.