Plastic parts for channels and window frame

To start, you have what looks like an 18-166 top sash guide. Compare the measurements on the site to tell if that's truly what you need. As for your balance, it's definitely 29" with a 2830 stamp option, but I need you to narrow down the balance Series. Measure the bottom shoe as depicted below. If your shoe measures 1-1/8" like the photo, you have a Series 390. If it only measures 1", that indicates you need a Series 351.

Comparison of the S351 and S390 balance shoes.