I'm not sure if this thread is only for ground-up mech building, though I do those too and will post some here later. However I also do a lot of take-a-crap-mod-and-make-it-good renovations. This is a recent example of one of those.
I saw potential in this Who Dares Wins 26650 mod, especially the form factor and material, and thought in the worst case I could use the aluminum casting and replace the main components. That turned out to be the case. Stock performance was poor, hampered by a typically weak switch (current passing through small spring) and iffy contact with the 510 center pin. I bypassed the stock switch and installed an LPG tube mod switch up top. It doesn't look much like an LPG switch anymore because I shortened the bezel so the button would sit up high. A quality spring loaded 510 replaced the original. There is one wire inside going from the bottom of the battery to the 510, otherwise the connections are solid and mechanical. Hits great and feels very nice in the hand. Been using it with a 4200 mah battery, but will probably try one of the new 5200 mah types. Total height to the top of the button is under 90mm.
I'm not sure I'm done with the finish with this one. All I did was chemically strip it, square up the top and bottom surfaces, soften the edges and give it a satin hand finish using different grits of metal finishing pads. The front seems to need something though. Maybe a big circular Lucky Strike sticker or a bulls eye?
$19.43 Who Dares Wins 26650 Mechanical Box Mod - 1*26650 / aluminum alloy / black at FastTech