Hi bill, last night I did checked with my car that the axles distance is about 200mm and the M300GT is about 210mm. I guess the 5mm offset from the front and rear axles should be ok since we can adjust and cut the wheels opening on the shell randomly.
Besides needing longer shell holding posts, not sure if there is other issue should be noted. ^^
i know a guy play at wan chai and hand make a longer 底板 (210mm) for his 12r5 then play normal mini car body....it is not very 難 make a firbe 底板 but it will make the 1/12 not fast as it use the racing body.....if want to play mini body for fun.....i suggest buy m300GT or normal mini car like m05 (FF) or VM2 (4wd)