tonzi, I haven't built a hydro system yet, but I hope to own one when I retire.
With all the central heat in buildings in Alaska, I would assume that Ghurds ECM motors would be pretty common, and easy to get parts and replacements for.
I would recommend designing to follow some well-established principles. Most Pelton/Turgo's Ive seen have a vertical shaft with the gen on top, and are direct-drive. Its not hard to find industrial motor shaft couplings, they look like two hands with fingers interlocked with a rubber "star" in the middle.
I would not hesitate to use wood and plastic in the prototype phase, there will be changes along the way. Once you have it sorted to your satisfaction, you can make a significant one with proper materials.
You said you have a penstock, is there a diversion creek for excess overflow (fish regulations vary?) or do you have an overflow pipe passing through your dam?
Even with the top half of your penstock freezing solid, I would have assumed your turbine feed-pipe draws water from a middle elevation of the penstock level. Below the bottom of the ice, but above the mud-floor?
60' of head is very useful, but on a slope, I'm assuming its a 200' (or so) run of pipe to the turbine? I'm going to guess the pipe must be insulated to prevent freezing in winter.
I don't think it would be too hard to build a Turgo from scratch. The way I understand it, A Pelton has split cups and the water jet shoots at the rim inline with the disc. Half the jet water flows to one side, and half to the other.
A Turgo has only one curve. On a vertical shaft hydro-unit the jets would be in-between the gen and turbine, the water would shoot down at a 45-deg angle, flow through a smooth 90-deg curve, and exit out the bottom. Using at least two jets (one on each side) would remove any side-loading on the bearing.
The prototype could use PVC pipe sections as the turbine blades, but stainless steel hydraulic tubing could be acquired for a more substantial unit. It would look something like this:
http://www.fieldlines.com/comments/2007/3/1/5259/19738/25#25
Buying properly engineered Pelton/Turgo "spoons" to attach to your own disc should be relatively affordable, but I was shocked when I saw the prices for these injection-molded plastic items. You could buy one, and make a silicone mold, then cast your own aluminum/brass (from cartridges?) using "lost-wax" method.
http://www.artesanto.co.uk/ho