[Graham]

3 cars per entrant...is a pleasant surprise  

Why only plastic chassis?  Is this because SRGB is plastic only?  This rule is definitely going to count one regular entrant out.

There are no team awards, so it would be a maximum of 3 cars if an entrant wishes. 

The reasoning regarding Metal or B&W chassis is that they do offer improved stability over non metal chassis, and in a proxy where stability is going to be the overwhelming benefit for success ( compared to others) I think this rule is important, in the same way that the motors will be restricted because of magnetic traction on metal contact rail tracks. The B&W chassis are not commercially available ( except Revoslots) so these chassis are exclusive to only one or two persons.
I have permitted them in a different proxy context, where I felt they did not offer such a significant benefit, and would do so again but not this one. And I believe that it is not necessary to have them included just for one persons preference. So I am sorry to that person if he can only build metal chassis cars, but that’s the ruling.