There are a number of variations of oil bowl from other models which will fit a CB750, and have I believe the locating pip for the crankcase lugs. Early Goldwing and CX500 come to mind, and I believe had some external / shallow fins. Sandcast crankcases of course have the two locating lugs, yet the early round bowl had no corresponding piece.
There does seem to be some debate about the correct round bowl finish, with reference being made to trying to achieve the cast finish by blasting, use of silver paint, etc, and I seem to recall the Yamiya repros to come with a "dull" finish.
Picture of original bowl from #302 attached. Clearly not externally sandcast, nor painted. When found, the bikes had less than 10,000 miles showing, had been un-used for 30 years and was VERY original. The "patina" (read crazed clearcoat) was the same on the oil bowl as on the various clearcoated engine covers, but with a touch of gravel rash off the front tyre.
For me the only correct finish (for #302 at least) was the same as on the other clearcoated engine covers.
I also seem to recall that some of the factory literature shows a bright, polished finish to the bowl.
Perhaps like other parts, different finishes came with different batches of parts?
A couple of repros I have made from damaged finned bowls have been done on a lathe. Only trick is to get it to spin true (I made a mounting hub up) so that you machine an even amount of all areas. other than that its straight forward to do (if of course you can access a machine shop!)
Cheers all.
