Rubicon ... I totally understand why you didn't fuss with the differences in engine access panels. As you said, if the opening was in the same spot, and it was a matter of having a one-panel or two-panel piece to insert into that space, then fine. But the opening is lower on the BA-3, and that means it gets tricky. As a plastic kit, you would end up with a seam where you don't want one, if you had to make two elongated parts to fit one opening, one with a single-panel hatch on top and a flat panel below, and another with a flat panel on top and a two-panel hatch below.
And there are photos out there supposedly of BA-3s with the single-panel engine access hatch. But unless you can see photos of the front and rear of the same vehicle (so you can see if the back has the door or not), then it is hard to fully believe those odd photos really are true BA-3s. It could just as easily be a BA-6,, but they had some old-style driver visors left kicking around, so they used one instead of the proper new ones. Or it could be that a BA-6 was destroyed (somewhere in the rear), and they had a BA-3 that took damage in the front, and it was easier to use the former BA-6 pieces in the front to make repairs. So those pictures could be of hybrid/repaired damage vehicles cobbled together, and not an "off the assembly line" version of the BA-3.
But hybrid or not, it justifies the decision to go with one type of engine access hatch. I have no complaints.
The main difference between the BA-3 and the BA-6 was the back. There either is or is not a door. Beyond that, you have the slight difference in the driver visor area, and the slight difference in the engine access area. I may change my mind with the kits in hand, but I plan to do the minor tooling necessary to the engine area to give me a close approximation of the engine hatch. I won't lower the opening, that is probably too much effort. But I think it will be quite easy to get a two-panel hatch in place of the single panel. May not be "quite right" as the hatch will be slightly higher than it should be, but it will give the model a third area to differentiate it from the BA-6.
And I won't be worrying about the bracket at the top either. At this scale, it would (at best) be a little bump of plastic not quite like a rivet.