That sounds really bad Chris.
I can do you a favour and take your Club 500 off of your hands for a fiver if you like so you can focus on making your new blue and white one from a nice shiny new kit
Meanwhile - I can't imagine that the type of radio used makes any difference as the only two functions used operate the steering servo and the speed controller and nothing else.
Some owners will prefer stick sets and others will prefer a steering wheel and most come with various additional channels for mixing etc that will remain unused in your Club 500.
I see the pictures posted here by Bustergrunt show a variety of different transmitters being used in their recent race meeting and they don't all look to be two channel sets either. I am sure that the transmitter choice make's no difference.
As a matter of interest I will probably also be using a RadioLink RC4GS as I already use it for racing 1/12 scale r/c cars and my other fast model boats. Only two channels are used on any of them!
I am not so sure about replacing the radio mount with plywood or not using the specified coupling - but I am sure that someone that knows a lot more about the racing rules than us will come along to clarify that for us shortly...................