RE: Rossi 40
Depends, there were several Webra engines that were used in quickie. Early on most just flew K&B engines, but then people wanted to start flying Schnuerle ported engines since they figured that if not used for racing they would be better for sport models than the weak K&B. So we entered the "engine of the month" club, which meant that people spent a lot of money chasing which motor that seemed to go well at the previous contest. ST, Como, HB, Webra, OS, Fox, and maybe a couple that I have forgotten all came and went. It got very expensive.
The really hot Webra was just introduced too late. So they may be somewhat rare, since nobody was looking for one after the Nelson came out, and I don't remember if they were much different in design from the earlier effort. One plus is that they are quite a bit lighter than the Rossi.
So I would put on a test prop that let's them turn up to16-18K and see which one runs better.