Concerning speed, I just can refer to BrianGs R/C calculations where I got 46 mph with my 11 pinion+46 main gear, but 11 is really minimum and everything stays really cool (really cold). There is enough power to gear up to .. maybe 14 or 15... but who wants to speed should take a 1515 1y. My setup is fast enough for me, and short gear makes a lot of fun on gravel roads :-)
Like Serum said, motor in front would be a better... now with the batteries (more or less in the middle) it got a bit heavy in the front. But this was the only solution to keep it compact and tiny. Mike announced a kit for the Savage but he is really busy and needs some more time.
Yes, maybe some extended arms (for christmas :-)... but more urgent will be a plastics or delrin spur, the pinion is getting weak already (nevertheles too much power :-))
yes indeed, 2 sheets of 0.3 mm, easy to cut, then a bit of glue on the TVPs, thats it. Then just make holes where necessary and screw it between the plates. I think it protects a bit better against all the dirt and stones flying around when you accelerate ...
well, there is no thread telling how long the drive shafts have to be... this is your decision ... you decide where you put your motor.
I did not like to have the batteries outside the TVPs, I wanted to have them inside the chassis, so I had to push the motor to the rear, the batteries to the front. As the motor is close to the rear differential, the drive shaft got short... and to the front it passes along the batteries, so it got long. I just measured the length I needed, and Mike fabricated the drive shafts (very well) (thanks again to Mike!!!)
motor in front ... but there is the steering ... this gets complicated .. or you loose a lot of space, I think the batteries will not match any more inside the chassis. But try it out, we will be curious seeing your version.