When using 2 belts make sure they are a matched set, and yes, when you call them ribbed, if you mean they have cogs, yes cogged is better. It's like the difference between totally bald tires vs new snow tires, they grip better. On my BB4 at 27" I used to add belt dressing, it also helps the grip.
I never saw 28" but 27" was common, and if it dropped to 25" it was time to check for leaks. The BB4 pump is a real workhorse, just make sure to chande the pump oil at least 2x a year and check the oil level daily. I used TSC oil without issue but I hear it is hard to get this year.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.