yeah there is a lot you can do to a stock cylinder first.
some people put playdo in the crankcase with the cylinder off or cooled wax- to prevent metal shavings from going off into the engine and dremel it down to match the cylinder-(just remember to remove the playdough afterwards! (the advantage of cooled wax is once you clean teh metal shavings off the wax acts as a lubricant so it can just stay in there-- you can also widen the transfer ramps on both case and cylinder. you can also cut the piston skirt by a few millimeters, lower the intake window, raise the exhaust port window by 1-2mm. i recommend the minarelli 15mm intake on a puch because they easily fit 15 and 16 dellortos and clear the engine easily. but you have a bing, nevermind. you can also shave down your cylinder head. anyway, all of this is easy to do- just be careful because a mistake can sometime fuck up yr cylinder. it is good to have a spare puch cylinder to do this to so if you fuck up you aren't screwed. anyway. there are a lot of posts in the performance section probably about this and im sure some portwizards could chime in here. anyway- 40's are definately doable on stock cylinders.