Not the point though. Whilst the engines might be
considered legal they patently aren't
original so with the greatest of respect you've already allowed a performance advantage into the series. The later Twink blocks are stronger than the originals. Its why the old Classic Touring Cars ran them in the early nineties.
So if that is allowed what's next? Etc. etc.
So I'm glad the series is giving you and all those with qualifying cars a place to race with a stable set of regs but as you say its actually no different from Top Hat, CTCRC Historics (App K) et al who also allow these mods. That then brings us back to the question. What's this series for?
BTW. I am playing devils advocate here. And knowing Smurthwaite reasonably well I'm
certain he wouldn't allow any of his cars to be anything but in line with the regs. But the regs will necessarily be flexed to fit the mechanical availablility, thus your expensive L/C or Alfa won't be quite the original car everyone would like to think it is.