I bought one of these, and it works fine, except (for me) the barrel is quite low, as Stephen indicated, and the eye relief can be a problem.
With this, you can only use one scope ring, and a compact scope (I wanted to use something light since it only had one ring holding it) was too far forward. A regular size scope would work, but it's still very low, and I don't think it's well supported for extended use. Never tried it, though. Maybe if you bought two of these and then could use a one-piece mount straddling both of them.
I also am thinking about how to use the bushings that come with the existing forearm. Let me know if you come up with anything interesting, and I'll be sure to do the same, as I'm actively working on this right now. I was thinking about cutting off the top of the forearm wood, re-shaping the whole forearm, and attaching a weaver rail on top.
A few years back, a guy("PALIK")on another forum used the Air Venturi intermounts that you may have been talking about. Pyramid Air sells them for about $28. They seemed to work for him after a bit of grinding, but the clamping legs did get a bit thin (maybe not too thin). Let me know if you can't find the two threads where he builds his gun and then solves this exact issue for himself. I have PDF files of both threads that I can email you.