Oilspot:

I have a 1991 M23.  The floor plan matches their 2720 model, so I looked at the spec of the models on TM's website and this is how I do the conversion.

The 2720 has:

Equivalent trailor size-open: 27'
Towing length-closed:           20' 3"
Bodly length-open:                23' 11"

Therefore, the new model number 2720 uses
Equivalent trailorsize/Towing length-closed spec for the model number.


Which means the old model numbers (M23) uses the Body length-open spec (at least the foot part of the measurement) for the model number.

Hope that helps

Gary