I'm transforming my 034 into an 036 as we speak. My goal is about 1HP gain. (1/2 HP from cylinder and 1/2 HP from muffler mods).
I really like the 034's and they seem to be a sleeper in Stihl's lineup.
I bought a 036 cylinder kit on Ebay and it fits my 034 like a glove. Fortunately my muffler also fits the new cylinder just by removing the spacer. (there seems to be lots of versions of 034 mufflers so you might get lucky).
I had to order a new cylinder gasket, new piston pin clips, a decompresssion valve plug for the new cylinder, and decided to replace the pulse hose just to be safe.
The shroud will need to be customized to fit the 036 cylinder but a die grinder or Dremel makes it easy.
My biggest concern was carburation but I plan to try the stock Zamas S19. I'd think there'd be enough adjustment range to support an 036 cylinder. From IPL's I see that the same jets are used in 036QS's and other 036 variant saws. However I'm prepared to replace the carb if need be.
I also found out that 034's lack the cooling plate between muffler and cylinder but 036's have it so decided to order one.
Send me a PM later in the week because I should have it done and tested by then.