My favorite "stock" Puch set-up in the mountains so far is as follows:
-15 bing, 16 intake (bored 14)
-High compression head
-Clutch balanced and lightened to 92g
-Home-made V-stack, or Bing high flow filter
-14/45 gearing on 2.25 tires
-Proma GP pipe
It's not that fast top speed, mid 30's due to the gearing, but no hill stands in my way and i keep up with traffic. It's a bit flatter by you so can run taller gears and a lighter clutch no problem, on the same set-up but w/14/45 and 80g shoes I'm pulling 40 @ 5600'.
What made the most noticeable difference in speed, easily the gears; what made the most noticeable difference in power, the pipe; what made the biggest difference how they worked together, the clutch.