this is one of those cases where the mic connector can supply rx audio even though it’s not listed or intended.
the mic connector routes the rx audio TO the factory mic PTT switch, which is multi pole (can’t remember the ‘real’ name for the many pole single throw switch). that PTT switch connects/disconnects rx audio to the radio speaker at the same time as engaging the PTT/tx circuit.
so, end result is, you can get rx audio from the mic jack. you don’t have to use the external speaker jack.
even better layout:
https://www.qsl.net/ta7i/index_htm_files/htx10.gif
good luck
kb0wlf