Good Morning,
The specific pairing of balance attachments are what determine the balance Series. Have you confirmed your balance attachments are that of the Swisco 19-018 and 15-005? If so, then yes, the Series 377 will work as a replacement. The "29 5" translates to the stamp option: 2950.
If you're uncertain about your balance attachments, you can always upload a few pictures for us to take a look.
i just bought a S377-30 balance from swisco and didnt realize that the top & bottom sash guides are also missing. I think this (18-042 : Top Sash Guide Pair, Pan Am) is the same as with my part but i need the bottom sash guide p/no: pls advise if you can give me the correct p/no: i dont have the original bottom sash guide.
Thanks
dexter