HPBCANADA.COM

There very similar, OPBRA did change a couple of engine spec rules.
(1) the motor doesn’t require reverse. It still must shift from neutral to forward from the drivers seat. Reverse is seldom used especially if the boat has the hole in the transom for the power trim cylinder. Racers likely grind the teeth off the reverse gear. I don’t think there is a performance advantage with original stock gears. TORC (CBF) may think differently, so let the other racers and the class rep know before you race.

(2) OPBRA allows a wider range of stock and aftermarket parts. You can use carburetors off a different model and other parts. You can use aftermarket parts provided the parts fit without modification. So you can run the large bore carburetors on an oval port block and any electrical components that fit. The gearcase gear set is interesting. Under OPBRA you don’t necessarily need to run the original gears that came with the motor. So you can run 2:33, 1:76 or 1:91 . The 1:91 is aftermarket while the other two were original parts . I can see this gear option maybe a benefit to a few and may have been necessary when there was a shortage of original parts but prop selection normally adjusts for the difference in gear ratio. I asked on this site if anyone had tried a different gear ratio and how did it work out. No replies to date.
So I would just advise the other racers and class rep what you are running prior to racing.
I don’t think any racer will care. They just want to have fun.