Okay!
The kit you pointed to includes a special shaft, that locks in 1st speed. I used it too, and modified it to get it working locked in 2nd. After that i used the stock transmission (bulletproof, only the 2nd speed pawl is a weak link (i modified it though) you are better of getting the heavy duty 2nd speed. Don't change gears for aluminum or what so ever. The stock gears are bullet proof. In the movie i was running the 2 speed transmission. you can hear it shift if you listen very good.
The things you need to make your drivetrain reliable are HB lighting cups (they are better than aluminum, because aluminum cups chip rather fast, and the HB is only 5 bucks and bulletproof..
If you get
this your diffs will be bulletproof for sure. No need to get a 8 spider, i am willing to give those things the stress test against the 8spiders and i know these 6 spiders will win.
You need to get aluminum diffhousings (not the cups) only GPM makes them.. They are 25 dollars/set and they will give your ringgear/pinion the stiffness they need. (other wise they won't last too long, because they can jump over eachother in an allmighty powerstart or superstop.. You might also consider getting a set of the heavy duty diff shafts/cups
I am using the old type of HB cvd's, and they are very strong. I modified them with a 2nd set screw and dremeled a flatspot on the pin that goes thru. MIP's and UE's are very good too
What do you want to run? how fast do you want it to be?
I do recomend getting a set of the UE shocks with Nova or FLM shocktowers (or use a silicone hose inside the stock shocks)
Have you got a savage allready or do you need to buy one? best option is to buy a K4.6 SS kit, it includes a rather beefy drivetrain, and a nice servo safer as well, you only need to modify the diffs, though those stock 6 spider diffs can take a serious abuse.
I know people in Germany who run their savage with a 2240 on 24 cells and drive it at 55mph+..
A 2240 on 18/20 cells is insane allready. You can get lipoly, but if you never tasted the power of brushless, you can make a nice start with Nimh's too