Ok, so does the IIC in Vegas count? Ok, the 416 did not win but 6th, 8th and 10th (3 cars in the A) for a team that, as far as I know, did only one (!) foam race the whole season is not too bad. Sure, I am not so sure what chassis and top deck they were running but since, as you so rightly point out, Tamiya does not have a specific foam car I would not be surprised they did not have very thick chassis.
The only chassis I know of that the team has as an option is a 2.5mm chassis, a whopping 0.25mm difference. It'll help but I am quite sure the car will be quite decent with the standard chassis with all the screws in. You may not win the IIC with it, but that is not what the guy asked is it?