dont know if the g&g mechbox is a 7mm or 8mm but personally, if you decide to keep the stock gears, i would ditch the bearing bushings for solid ones (assuming the mechbox is a 7mm) i'm kinda affraid of those bearings bushings, because if they fail, the whole gearset fails too. i got a g&p drop in mechbox for my scratch build and i did not even fire a shot through it before opening it and changing the bearings for plain bushings and of course a new shimjob,

just my 2 cents!;)