It may be a little early to get upset about this.
JD is only trying to show you easy ways to substantiate your ride. He's had to do it himself. And successfully. before you modify the body into its race car mode, take some pictures with measurements visible -- maybe even with the old wood still in place. Are you leaving the wood in -- or are you replacing it with metal reinforcement?
The whole idea is to show its stock configuration. Being wider than an Essex or '23 T is not the point. Being creative and using something different is great. But after you've straightened it all out, patched it, reinforced it, and smoothed it, and painted it, it may be hard to see it's still stock. And the inspectors (and potential protestors) are not familiar with the dozens and dozens of makes of roadsters. And when you start kicking ass (which is not exactly easy in MR classes), it'll be easier to show them what you started with.
Take his advice and join the fun.
Stan Back