Heathkit HW-16 Help

[T23]

I have a Heathkit HW-16 transceiver, when I bought it, it. Was advertized as having an AM transmit modification. So. I can see some add on boards inside on the receive sie that aren't in the schematic or any of the diagrams, so I can't find this modification on the internet. I need to find out where thee audio input goes for AM. These add on boards look very professional.

Any help would be appreciated.

T23