The rule wording is too ambiguous if that's the case. It should just state something to the effect that unmodified, stock suspension bushings are required.
It's meant to allow for OE-replacement bushings that are not from the OEM, as tends to be required for many vehicles where you can't necessarily get original parts any longer. The rules are very clear on the "unless explicitly stated, it is not allowed" on every single category.
All that said, unless the car is a dedicated autox car, don't let your class define you! Do what you want with the car, and just drive the appropriate class that results. Unless you're actually going out to nationals and trying to finish in the top 10, it's not going to change your experience significantly. I ran what should have been a very not-competitive Subaru in ESP for a few years just because it had a modified ECU tune - not for power, just because the stock tune had detonation, so I actually ran lower boost and a bit less timing. It was still a ton of fun, just made you want to drive that much better.