Well, preliminary experimentation has shown that it might very well be possible to use 4-Tec steering blocks TRA4336 to convert a Stampede into a 4X4. They already carry 5X11X4 bearings and the stock slider fits through it nicely. It causes the pivot point to be roughly lined up with the U-joint. This prevents the steering from swinging the drive shaft into the shocks.
There will need to be some slight modification to the stub axle. The hole for the pin is too far from the outside bearing to prevent axial motion of the axle. A hole drilled through the stub axle closer to the yoke end will solve that minor problem. It also will allow the axle to extend further through the front wheel which will allow for more thread engagement with the wheel nut.
I cut a stock caster block up to accept the 4-Tec steering block. I have it in upside-down to keep the steering block more inboard. I also used the 4-Tec steering block upside down to align the U-joint with the pivot point better. It also pushes the steering block outboard more. This may be an area that deserves revision or at least another look.
It appears that the 4-Tec blocks will still be wider by about 0.2 inches per side. That may be unacceptable, but time will tell. I still need to obtain more parts to complete the experiment. I am sure that the front will have a wider track than the rear, but this could even prove to be advantageous.
Of course one could use 4-Tec blocks in the rear as well to make the front and rear tracks the same width. Plus, there would be adjustable rear toe!
As this experiment progresses I will keep you posted and will get pix up if it proves worth the trouble. I really like this deal because wider is better! And it will keep the ol' 'Pede all Traxxas. (Well, except for the chassis as that will have to be custom.)