Never underestimate the power of cardboard! Personally, I found one of these PVC flanges laying by the side of the road. I use it like a pedestal to keep the scratchy bits of a hub off the floor or tabletop.
From a purely mercenary point-of-view, Abner serves as a showcase for your new tank. Do you really want to distract from that focus by adding the rack? The final decision might depend on the saddle you choose--it certainly did on Speedline BRAT.
That heatsink idea is beyond clever! I was thinking something along the lines of a ribbed rubber floor mat, which would be a lot easier to source and work with...not to mention cheap. I have one here I keep my wet shoes on that, apart from being black, looks just like those fins.
Those break-away pins are slightly tapered on the discarded end, making them much easier to insert and align. Discrete pins are necessary on a chain made of half-links because a typical master link can't be used.
I expect that would be very difficult to achieve with basic hand tools. Some bike shops have a frame straightener with an adjustable fulcrum. That might kinda work.
I'm definitely down to learn more! I've got one of the 'legacy' machines--an Expression--that I've hacked to use Sure Cuts a Lot and other software, rather than the proprietary cartridges. I also dabble in Inkscape, to create and modify the vector files that you're talking about.
Have you...
Maybe check with these guys? If they can't supply you with the proper seatpost, they can likely measure it accurately, at least.
http://worcesterearnabike.org/
Seatposts are sized by their diameter in mm and their length--there are many sizes. Some are quite common; others are oddball. If you're lucky enough to still have the original post, the size is typically engraved or laser-etched somewhere near the markings for minimum insertion...
This actually begs a question: Could a skip-tooth chain be 'revitalized' by replacing worn pins and rollers with parts cannibalized from a modern 1/8" chain? Has anyone even tried?