The motor is a slightly different design. It is round compared to the flat sided blade motor. Toprudder is correct about the higher rpm rotor. The tail responds faster, so it doesn't have to work as hard. I didn't use the GWS mount. I just removed the stock one and flipped it over, then cut out a little of the housing to accomodate the round motor. The advantage of the GWS mount is you get the tail fins with it. I had to buy mine separately. I got mine at the lhs in Jacksonville and they didn't have the mount in stock, so I improvised. The biggest advantage is not having to worry about the gear slipping. I use the GWS 3" push on blades with mine. I bought the 4" with prop adapter but haven't needed it. I've only busted one prop and still have the first motor on it.

Here's a link to the part numbers from bladecprepair (use the search feature at helidirect, etc. for the parts):

http://www.bladecprepair.com/man_tr_dd_conversion.html