As for the engine upgrade you can buy the .18 piston and sleeve but you may also need the .18 cooling head as well. I didnt know this and just got the .18 piston, sleeve, and connecting roda nd the engine had practiacally no compression. I have heard some people say that they got away with just putting in the piston and sleeve but it sure didnt work for me. A better choice is the OS 18 CV-RX. I just put one in my MT2 and it has a TON more power. I havent broken any drive train parts yet due to too much power. (after I did the diff cup mod). I wasn't able to get my front wheels off the ground at all with the stock engine and wheels but after the OS .18 and some masher 2000s it wheelies nicely.
Also you may want to think about the aluminum brake seat, it makes a huge different. You may notice with the stock one that the rear of the chassis flex's a bit (although the roll bar helps). After the metal brake disc and aluminum brake seat, i have to be careful not to fully apply the brakes because they will completely lock up and make the MT2 do an endover. It can do some sweet stoppies now though Also do a search for azzman's fuel tank mod. He made a nice step by step with measurements to replace the puny 75cc tank with a 125cc ofna tank. Sorry I can't tell you anything about the spurs/pinions. I just left mine stock.
Good luck. These FF series RC's are wicked nice for the price.