Need window channel guide for bathroom window

A quick learner from St. Pete, FL says:
I need to replace the window guides in a bathroom window. The specs seem to match 17" Series 390 Channel Balance (the shoe is 1 1/8 inch deep), but for two issues: (1) the metal to metal length is exactly 16.5, not 16 and not 17 inches. And stamped on the metal is 1620B. (Photos attached.) Thanks, you've been so helpful in the past.
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Tom from SWISCO responded:

Hello! We can supply this balance, but it will have to be a custom order due to its length. What I'll do now is email you a purchase link and price quote that will allow you to add 2 of these to your cart. You can then checkout as normal.

To summarize, these will be a 16.5" long Series 390 (measuring just the metal channel) with a 16205 stamp, which should be the same as your original.

Please let me know if you had any questions or wanted to make any changes. I would be happy to accommodate you.

A quick learner from St. Pete, FL says:
Thanks. The custom piece is a lot more expensive than the stock piece. Would the window likely function adequately if I simply opted for the 16" stock piece instead? This is a seldom used bathroom window.
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Casey from SWISCO responded:

Hello,

Tom is out of the office today but I can tell you that the length difference, if you tried to use our stock balances, would most likely not hold up and could break shortly after installation. The pulley travel length will be too short without the extra 1/2" to compensate. 

A quick learner from St. Pete, FL says:
Thanks for the explanation!
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