Hi kroll62!
You may get them here...:
http://mfz-blocher.de/getriebemotoren.html
The 75:1 will work well also...
They have enough torque and the current is not too much. I run them with a 10 or 12 Amps. speed controller...
But the power of my Massey is also a question of tyres...them on the rearaxle are very soft (25 shore).