Yeah, I contacted multiple dealers across the US and nobody could give me a straight story. One really engaged with me, and said he would contact his Hobie rep. But even there after a week of back-and-forth he said we was getting "conflicting answers" and could only recommend the original, plastic cartridge.
SLH was able to immediately give me the low-down on the universal cassette (i think it is the "eclipse" cassette in the US) and which boats it would fit (including my iTrek 11) and this is the motor I ended up with:
https://slhobie.com.au/shop/kayak-fishi ... yak-motor/I was originally going with a Watersnake 24/DIY approach which would have cost roughly $200 all-in plus a lot of annoying labor. Now for $371 (in Aussie dollars!) including shipping, I'm getting a pre-built little bugger that looks like it will suit my needs perfectly all for only $65 more than I was going to pay for DIY.
Thanks again for that link.