Glad I found this as I'm looking for exactly the same clarification. Hoping this reply will bump the thread for more visibility and elicit some feedback from those who might be more versed in the rules and/or this specific setup.
I read the rules the same way in that Jager's captured steel guide rods would be legal as they don't require a slide insert/adapter to work and that RSAs made of material no heaver than SS are allowed. Based on all the data that I can find on the density of steel, stainless seems to be more dense than carbon and tool steel; as long as Jager isn't making them out of high speed tool steel then I can't fathom they'd be more dense or heavier than stainless.
The only rule that I could conceive would even come close to being infringed upon by the .270 rod would be 8.1.7.2, but I have a hard time believing that this would be considered an add-on weight.
I'm looking for the same benefits as far as tune-ability goes but don't want to break the rules to get it.
Thoughts from the experts?
