Something like this has been rolling around in my head for many years. I’ve always wished Tascam would have made a 1/2" 8-track head with a 9th and narrower center track for recording a sync stripe, much like many half-track mastering heads are made. Of course it would be incompatible with any other 8-track on 1/2" format. I just hate wasting a whole track for SMPTE when a track the width of a cassette track would work just as well.
Teac made a 1/2" 9-track head for some of their low-speed data logging machines. I doubt they would be up to spec for music recording, but I really don’t know. Mostly I just tell myself to stop obsessing about one extra track, but since I’m a screwy musician with a classic artistic temperament I can’t stop wondering about it.
By the way, for those who don't know, the MIT grad who modded his 1" 8-track to 1" 12-track was Tom Scholz, founder of Boston. The only thing is though his Scully 8-track was easily modified with parts available from the factory and the rec/repro amps were modular, so he could simply add four more to accommodate the new 1" 12-track heads. And yes he actually did track the Boston debut album on that machine in his basement studio using 3M/Scotch 206 tape. So one of the biggest selling albums in music recording history technically started in a home studio on a machine that was a bit worse than a Tascam 38 sonically speaking. (Something to think about)
So with the modular concept in mind I suppose one could use the transport from something like a Tascam 38, mount the 12-track heads from the Akai in the headblock of the 38 and fashion a cable for send and receive to the Akai electronics. The trick would be impedance and level matching due to the length of the connecting cable and eliminating interference in the cable. But plenty of older reel-to-reel machines had this modular design with the amps separate from the tape transport, including the Tascam 70-series and various machines from Ampex and others. Using the 38 you could even tap into the remote control interface for the transport and use the buttons on the Akai to engage Rewind, Fast-Forward, Rec, Play, etc. Fun idea.
Below is a Scully like the one Scholz modded.