Hi Joe,
Yes, this is Tamron Popular 400mm f6.3, and it is pretty awful optically.. but very good mechanically.
I tested it some time ago.. see thread here:
http://www.iceinspace.com.au/forum/s...hlight=Popular
But, it should be OK as a guider.
I also removed the tele-extender group from the lens (it was slighly damaged by moisture, a bit foggy).. and because my guiding camera is Philips Vesta housed in home-made enclosure and because the chip is close to mounting flange, the focussing is not an issue.
Focusing is as per normal - the screws holding the lens in place have nylon pads and are not tighten too much, so the lens can rotate in ring.
I used ABS for printing (and my home made printer so there is no cost here.. at least I do not take it into account), this plastic is quite strong (Lego is made of the same stuff). I already made couple of adapters for finders and never saw any issues. It is important to use 3D printout only where appropriate, and i feel it is OK for this application. Time will tell :-)
As for flexures, the screws are placed in ferules acting as bearings.. so I hope for the best
And springs are pretty strong, they easily carry the weight of that lens.