I'm not 100% sure about the Stampede, but my Nitro Sport and Rustler were both pretty straight forward swaps. I recommend the drive shafts and idler gear from the Slash 3.3, 6852X for the shafts, and 4496 for the idler gear. Also, being as it's such an old version, you'll probably want the newer...
From reading the info on the Pro .15 page, it looks like you have a short shaft. When I upgraded my Pro .15, I just threw a 2.5R in and called it a day. What engine are you looking at? Remember, if you go with a 2.5 or 3.3, you'll need a conversion kit.
It looks like you're missing the spur gear and slipper clutch. If you look at the parts diagram, you'll be able to see what's missing and then get the part numbers for what you need.
Like I said, the Stampede hasn't changed too much over the years, so the parts from a new one will probably fit your old one. I'd start by looking here and comparing the parts diagram.