390 balance with stamp 27D and stop

A professional from Illinios says:
I have some block and tackle channel balances that have a stamp of 27D on them. The true length of the metal channel is 28". Your model # 390 has the same plastic ends. What length of balance should I order. Also can you identify the balance stop in the picture. I believe your part number 18-031 is the correct one.

Thank you Pat L
user uploaded photo of channel balance and guide
Profile picture of Donna
Donna from SWISCO responded:
Hi Pat,
Looking at the sent images it does look like the 28 inch Series 390 balance assembly. Choose the Stamp option 2740, this is the equivalent to the 27D stamp.

The top sash guide, looks like the 18-033 or possibly the 18-031. You will need to compare the dimensions of your original to the detailed product images we provide online.
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