It's definitely a distributor. But yeah, the guy is probably 1/2 right; it's from a S15, just not a DET. A standard DE, sure.
Rotate the wheel some more. This also may be a 360/1 (where 1 slit is larger than all three) which signifies TDC.
ECU really only needs one reference point for TDC, and it just counts the slits for the remaining 3 cylinders.
https://www.diyautotune.com/support/...rt-your-240sx/
Don't think any SR or KA used batch fire (unless the KA24E maybe??)