Gates do supply belts to some manufacturers.
If you ran the Ferris number through the Gates interchange app and it came up with that belt the that belt should be fine.
Blade runner belts are kevlar fibre cotton wrapped belts so suitable to be used provided they are the same size and section.
I use Gates products exclusively on all my vehicles including my lawnmower (but Gates V belts there). I run Fleetrunner Green Stripe serpentine belts on all my vehhiles and either Gates white stripe, red stripe or green stripe hoses. Gates makes the best available and O'Riely sells Gates.
On a 178" belt 1" or 2" will not make any difference.
I would have gone for a strait 178" belt which being a standard size should be cheaper.
Down side of the computer age is any buffoon can plug numbers into an equation and come up with a result only an idiot would accept.
The 1/4" would be equivalent to loosening the anchor bolt on the tension spring 1/12 th of a turn.
