Greg, Bob, & Jake,
Thanks for sharing your point of view. I have to admit that I am fairly naive when it comes to "creative interpretation" of the rules, and that I should spend more time considering how a rule could be exploited before posting my opinion on the subject. If there is one thing clear about Bob's post, it is that the rule would be picked apart and exploited to its fullest extent. As a newbie to IT, I guess I'm just not in that frame of mind.

For what it's worth, I suggested that the diff could be allowed in the "notes" section with the following in mind:
  • A few IT cars are allowed such things at alternate bearings in the "notes" section
  • The 1.6 Miata rearend is a known weak point
  • The SCCA has already acknowledged this by allowing the interchange in other class(es)
  • A fellow ITA competitor lost his 1.6 r&p and diff during qualifying at the Cheap Date
  • The rule proposal is to specifically allow the rearend from the 1.8 Miata, which is also an ITA-classed car
  • The chassis of the 1.6 and 1.8 Miatas are otherwise exactly the same: the required OEM part(s) "bolt right up"