1955 counter weight

[Roy B.]

The original heat riser 1955 Corvette or Car only! had a part number CAST in to it , not like the repro. GM 12 above is the casting number of that moulding it came out of. You may see GM logo having different numbers discribing which casting Or mould the part was made in .
The reason was, if that part had a casting flaw with a GM 7 they knew which mould was to be destroyed GM 7.

That is all the number means after the GM

[Roy B.]

Re:Brake cylinder

Every original C1 wheel cylinder I've seen well have the last three numbers larger.
Parts number ending (even "o") tells you it's a right side part (wheel) ,if the part number (ended in odd like 1357 or 9) it would be the left side. Only a part that could be used on ether side the last number don't matter or a part like a Dist cap say.