Q:  I'm sure the frame I have is a Trackmaster - how can I tell?  Is there anything that ALL Trackmaster frames have in common?

Most Trackmaster frames have a continuous frame tube running from the steering head under the tank, down the back of the engine, and down to the lower cradle tubes' cross member. 

The swingarm pivot may go through the main tube as well. 

Trackmaster's all use a tubular swingarm - ROUND tubing.

Most did not have an integral rear frame hoop to mount the fender and/or seat.  The hoop attached at the upper shock mounts with bolts.