Henry:
If you decide to go with the B-26, I'd suggest you order one from Mike and be sure of what you are getting. The ChiClone B-26's are not uniform in size tolerances and ordering parts you will need for a basic tune can tricky. This I know from personal experience. I purchased an un-tuned B-26 strictly for the purpose of having a clone of my Beeman R9 to work on. After putting 3 different seals in it, replacing the spring with a Maccari spring, and going over the gun 3 different times, I gave it to a friend. It was shooting OK, but not anywhere nearly as nice as the MM B-26's I purchased afterwards (177, 22). And I wouldn't have done that well without some good help from a couple of guys (Bob Werner, J Woodcock) willing to give me more than a little help with the project.
I learned quit a lot and would gladly do it again. I now feel pretty comfortable working on my own air rifles, but for the cost of building my own spring compressor, the parts, lubes and the tools I ended up purchasing to get into doing work on my own air guns (digital caliper, brake cylinder hone, Dremel tool and bits, brass hammer with punch and drift set, metric and SAE allen drivers and gunsmith screw drivers) and the time spent, that first B-26 was a pretty costly learning experience. Unless you want to get really serious about working on your own air rifles, and perhaps already have the tools at hand, purchase the B-26 already tuned and you will come out far ahead. Mike does a great job and at a very good price.
I also have a Diana 34 Panther 34 / 22. The Di 34 is a good shooter and off a rest, it will shoot single hole groups at 30 yards. But it is longer, nose heavy, and requires much more practice and a very precise technique to shoot off hand accurately compared to either the B-26 or the R9. Either is plenty powerful. I would advise waiting on purchasing a 350. Supermags are a hard first air rifle to master.