First one-- the extra cc's comes from the motor being resleeved to accept a bigger bore and also having a new crank installed to increase stroke. Second one-- a 305 kit can be done (hopefully) by any accomplisehed mechanic. Simply tearing down the top end, having it bored and properly reasembled should take care of that
third one-- both the 305 and 330 could either run on reg gas or race gas-- depending on the compression of the motor-- higher compression means you have to run a higher octane fuel to keep the motor from knocking. Even going to a 10.5 to 1 comp piston should add some snap to the lowend yet still enabble you to get by on 92 octane gas.

 

I dont think hat you have to actually purchase a kit for the 305 motor. All it takes is boring out and then a new piston. I am getting ready to put this in mine and its only going to run around 150-175. Basically the cost of the piston kit and then about 40 bucks for the bore job.

I am getting an 11:1 compression piston and will have to run premium gas and maybe race fuel. But definately premium so that is soemthig to think about.

 

Hey dude I have a 350x in the 250x frame i think it is better than the 300ex simply because it is stock 350cc which is more stable than 300cc modified to 352cc. Plus you can buy a new 350x motor for under $1300.00. Or you can buy a used 350x complete for around $1300.00 than you have a frame to put the 300ex in and sell it for $1300.00.It all adds up.Also if you want the 350x swing arm can be made to fit the 300ex frame with a little modification. The 350x swingarm is about 1.5" longer and it has a better shock. If you decide to go with the 350x e mail me I could give you the details.