I like the Mambas too. The 8XL will be the perfect motor too. I do, however, thing that the 17/44 gearing that you want to use will be a bit too much gearing and may cause a small problem that may manifest itself in the form of some cogging. You may want to start with something more like 15/46. I'm not saying that you can't use a 44T spur. Perhaps something like 12 or 13 or the pinion with the 44T spur.

I'm only mentioning this because it's a problem that I had.