I think dollar for dollar #3 would be the best choice. It looks like the owner took good care of it and didn't thrash it. The oem swingarm looks to be in good condition. At least from what the picture shows. I think they are a little high on the 10k invested but I guess if they paid someone to do all the labor. As far as the 350 goes it all depends on the porting as to weather or not it'll make a good trail bike. My 310 is waaay to much for trails. For the price of the bike though; you could easily sell the jug on e-bay and buy another jug with a smaller bore. That may lead to troubles because of the case being bored. It may be easier to remove the strocker crank and spacer plate, I think that can be done without f-n up the port timing. Either way, I'd go with #3