Non mirrored JBL 4312...

another words, the woofers are symmetrical, but tweeter and mids are on the same layout.

You could try to swap the midrange and tweeter with each
other. I know the cutouts are different but it could be
done.

Also, a lot of the early JBL speakers were made to sit
upright OR on their sides. If you placed them on their
sides, it wouldn't matter because the mids and tweets would
be in the same location. Low frequencies are non
directional, so it doesn't really matter where the woofers
are on the cabinet. In this configuration, one woofer would
be on the outside and one on the inside.

You could also just toe in one speaker a little more than
the other to align the tweeters with the listening position.
It will look kinda funny, but would accomplish the same
thing.

You start swapping drivers around and you'll never sell them. Just leave them alone and hope for the best. I highly doubt anyone who buys those speakers would hear the difference anyway.

Well, while I'm not audiophile but clearly realize the soundstage is jeopardized and it's audible. The feeling that you have to use balance control even when played mono to 'move' the soundstage.
I'm in between swapping with some additional cutouts for tweeter spot to place mid-woofer instead and flipping front panel. Tweeter inserts onto the mid-woofer slot no problem.
Flipping the front panel would be ideal case only I have to de-couple it from the rest of chassis which is quite risky.
Placing the on their sides is common practice and I'm aware of that, however it still requires drivers to be mirrored.

Turn one of the JBLs upside down. Then they would be mirrored.