Update and a tip to others looking for parts:
A full month later and I'm still not trolling
... emailed the folks at Fish307 with the same info I posted here - got a response back "XXX part number is exactly what you need". So, I ordered it. 4 weeks later it arrived - and it's only 3/4 of what I needed.
So, after looking at the diagram again, I found the couple missing parts I need. Another order in - we'll see how long this one takes.
The moral of the story? Don't trust customer service only - double, and triple, check the schematics to me sure every last clamp, nut or bolt of what you need is included.
Between time spent, shipping charges for multiple orders, parts costs, etc - I'm wondering if I wouldn't have been better off just buying a new set of downriggers (or at least something "complete" off craigslist). Just hope the fish are still biting in August