340 pistons

[arizona satellite]

I am working on a friends 340 thats in a 63 dodge D100 and while replacing the oil pump came across 2 sets of part numbers cast into the piston's one is 3671154 and the other is 3671155. I understand that the 54 is 1971 floating stock, but is the 55 a serv replacement? I can't imagine them being an overbore piston. please help shed some light on this::hello2:

 

[Sublime440]

Did you measure the bore of the cylinder? I think a stock 340 bore is 4.04"

 

[arizona satellite]

no I was looking at them from the bottom while I was changing the oil pump. from what I have found the part number is a std 340 while the other part number seems to be a std serv replacment.