82B would indeed be a 1928 model.
I've not really seen anything posted that confirms the serial number, unless thats the 10673 that you're referring to. The fact that that number is there leads me to believe that it was not originally built as a Racing Chief. The BR's never had any letter designation on the rope sheave, and the only number stamped on the crankcase was usually behind the carburetor just below the magneto plate, and these were almost always a three-digit number.
For what its worth, there's no record of the Racing Chief being available in 1928, in any way, shape or form. Obviously, it would be possible for somebody to acquire the necessary internal parts to make an 82B into a BR, as its simply a matter of plugging the race parts into the service crankcase. I'm not sure if the Racing Chief crank used larger diameter bearings than the service Chief, but Jim Ross would know that.
And a Racing Chief would NOT have that big flywheel and armature on it. Lockwood instead used a variety of the Ace flywheel that was balanced differently for the Racing Chief. They also therefore had to use the Ace rope plate, which had no spaces provided for model or serial numbers. There's also nothing to support the notion that a Racing Chief would leave the factory without being equipped with the round cylindrical tank, dual carbs and linkage, and drip oiler(s). I can see somebody exchanging the dual carbs for the single, but why get rid of the oilers and round tank? Because they wouldn't.......
There are a number of circumstances that could explain this motor. If it is indeed a 1928 motor and has racing motor parts in it, I would bet that they most likely would have been installed by somebody trying to hop the motor up from a standard fishing motor to something faster. Lockwood sold a kit for converting the 82B to a 92B with underwater exhaust, you had to change the lower unit assembly and add the exhaust T-pipe. The only things left to swap would be the intake manifold, carb, and throttle handle; if those were upgraded to the newer version, in short order you'd have an 82B with all 1929 features. I'm sure a person could also buy the Racing Chief parts to build up (or rebuild/repair) their own motor if they wanted to spend the money.
It all hinges on whether or not the numbers stamped into the crankcase match the ones on the rope sheave.
WRT the aluminum rods versus bronze - I do not think there was such a thing a "racing bronze rod". There may have been bronze rods that were modified by racers, but I don't recall seeing any listing in the Lockwood parts books for bronze racing connecting rods. The Racing Chief was supplied with aluminum rods from the factory. These were not very durable and them letting go during race conditions most often is the reason for so many scars and weld repairs being visible on surviving 92BR's today. The aluminum rods that didn't break were usually replaced with the service bronze rods for reasons of added strength with the penalty of added weight to the reciprocating assembly.
Disclaimer - if you talk to Jim Ross, and he tells you anything different from what I've written here, go with what he says, because he knows way more about the Racing Chief stuff than I do.
Hope this helps.