Rather than pollute/dilute the ethos thread, let's discuss this here.
The reasons I gave for allowing the "approved" modifications include;
Removal of governor, costs absolutely nothing, allows the engine to operate in a band of revolutions greater than approx 1700 (from idle to governor cut) and also lengthens the life of TAV belts as they are not subjected to as much slippage
Alternate air cleaners, in some cases "packaging" of getting the power unit into the car, cost is minimal, and yes they do allow marginally better breathing, but also better air cleaning/filtration
Alternate exhausts, packaging mainly, a number of desirable looking cars look absolutely hideous with the stock exhaust. Some alternates will give more power, I suspect some may be worse!
Carburettor change. If you have ever had to mess with the stock ones, which in some cases you can't even get to some of the jets to clean ethanol deposits from, you will understand.
Flywheel, some clone ones have exploded. It's right behind you, "nuff said?"
Of course one of the major reasons was to be inclusive of existing CKs, as I was attempting to do to allow for Chris' plans for his scooter power. When the guidelines were framed every engine I knew about already had the changes which are well accepted in the US, and regulated.
If we were to say that buying another engine was a good option to participate in other events, I suspect that some would decline taking part, and some (me for instance), would decline cos it won't fit in the car with the rear cover on.
I'm guessing that even changing the tank could be said to be "not stock"?