Small Engines (Lawn Mowers, etc.): b&G MOTOR, vertical shaft, model numbers

Question
what  the difference between Model# 28T707 and 28m707 b&G  MOTOR?

Answer
The real way to identify the difference, if any, is with the type number.  Both of the model numbers are 28 cubic inch block, vertical shaft...check out this link for the rest of the model number identification.  
http://www.briggsandstratton.com/display/router.asp?DocID=65324
Are you trying to swap engines?
Eric