No pictures visible to me either.
Here is a scan of the Gilbert American Flyer factory service manual page for a 21206 power unit.
According to the manual, there is no frame. Just bars that snap into slots on the cab. I have seen a few Gilbert AF locos put together this way.
Here is the link:
Gilbert-21205 (also 21206)
Didn't see a diagram for the motor truck itself, but I could have missed it.