Hmmmm ..... interesting. So I had a quick measure up, ruler not vernier. The T28 tracks are around 6.7 - 6.8 which is just on 19" so a touch under and the M51s track is maybe a little over 8mm which would be close to the 23" the HVSS track should be. Not perfect but given the T28 is a straight wargaming piece (tracks and hull are 3 pieces) and the M4 is supposedly an "scale" model I'd say both are close enough.
The T28s definitely look smaller in the pics for some reason though ...... the pic was just meant for approx comparison at any rate and at least I left out my 1/76th stuff!!!!