rm 125 big bore kit?

all you need to do is go to ericgorr.com he will do everything you need and it is really affordable believe me it is worth every penny to send it to him. I think his 134 and 139 is like 385 or 400 and the 144 is around 450 or so thats with a piston head machining porting and the new radius on the powervalve that is needed to match the larger piston.

the $450 price is for modifying all the parts needed for your or someone to put on your bike. you need to send your cylinder and head to him for the modifications. if you put what state/city you lived in your profile someone could reccomend a good shop to put the parts on.

the kit you mentioned above with the sleeve will still need to be installed. sleeves typically are not as good in the heat transfer. not really what you want when you go to a big bore. Eric pretty much invented the 144kit back in the 70's. he is the guy you want to do this work and his prices are super competative.