According to Francillon, The Betty Yamamoto was shot down in was a Model 12.
The Model 12 which was usually designated just "G4M1" and was an upgrade to the intial production model ie. the G4M1-11 HTC is implementing.
Well...

If you're gonna nitpick....

This one Francillon got wrong. He's made a couple of mistakes (misidentifying a photo as the wrong squadron is another I read about today). Overall seems a good source though.
There was no "model 12"... There was no new designation on the model that had rubber panels underneath the wings (to protect the fuel from ground fire -- but not from above!), and the "larger" superchargers (I assume that means more powerful, not that they took up more mass?). These models were in the end slightly slower and had slightly less range (hardly worth mention) than the other "Model 11" versions. They had no designation except in a few technical orders for parts and maintenance. They were still simply the 11. On those rare occasions when paperwork had to differentiate them, they were "model 13" and the only time "model 12" was used was very briefly for the G4M2 prototypes, but these were very quickly renamed the "model 22" instead.
So, no Yamamoto was shot down in a Model 11, just a slightly differently configured Model 11, hehehe...