Sounds good Miles! I'll get to work on it. I have a small block LR kit that I really dont ride much (Kansas is as flat as the USA economy), so I anticipate using the stock belt drive primary. I'll be putting a chainring on the left side of the rear wheel, but keeping that chainring reasonably small will allow the chain itself to pass between the chain-stay and the seat-stay without any off-setting idlers needed.
I don't have to wonder "if it will work". I am certain. I just want to have a bit of fun, which will end up with a working prototype. I've been disappointed that there hasn't been more interest in Thuds 2-speed dog-box. Its absolutely brilliant. That being said, I think this version "might" be easier to DIY. Mike Backus is recommending 219 chain and 15mm shafts, plus he's willing to make any custom part to "fill in the blanks". Of course the less custom "one off" the parts, the better...
He has small driver sprockets in 12T, 15T, 18T. Here's a pic of the 40T sprocket he's begun producing already, which is barely larger in diameter than the W-I flanged ENO. A 40:12 first gear would be
3.3:1... Mike mentioned that there are no other sprockets readily available between 18T and 64T...
I recall liking how this builder used a shaft clamp as a bearing holder:
For the newer members who aren't familiar with Thuds 2-speed, here's a pic of that particular juicy steak:
