I would aslo if possible check into how Beefy the Crank shaft is. Your adding over 100cc from the stock size. I no some cranks are very liteweigh bikes no days . Back in the 70's and 80's Manufactors were not to concerned with weight of bikes. Now they are building bikes so lite..... I learned this with the Busa which is a Rocket but I no many guys that did lots of mods including Nitrous and Big turbos as long as they kept the tire around the stock size which is big anyway they had no problems. Now remember the crank was not stock it had been balanced and welded for strength. But soon as they add a big sticky tire or a 10" car tire like I had they would fail..[]
Now I no were not drag racing our bike but if you add more torque and power and are spinning in mud and running a high rpm then you catch a rock or dry dirt and get some big time traction thats what is very hard on a crank shaft....
I'm not saying a 380cc kit won't work but just keep other main parts in mind....

 

I'm sure you guys are right. I did ask about the higher bores and Kustom Kraft's response was that they do a 330cc bore but no larger - he said the higher bores sounds like a Stroker motor and I believe you had to send your whole motor to them and they did replace the crank and rod with stonger components. I think 330cc would be OK though. I don't want to have to pull out and ship my motor somewhere - that sounds like a lot more money and time. I'm going to wait until the weather turns bad even before shipping my 300cc sleeve.

And if something goes wrong, I still have my 250cc sleeve and piston as a backup.