Voyeur, I did mine freehand and while it wasn't perfect it did the job well. As long as you drill the hole a hair bigger than the nail, you'll be OK. Ranchero listed the drill bit and nail size needed.
On the hinge pin, it looks like there might be just enough room that you could drill a hole through the pin between the hinge and the spring, then a cotter pin can be used to keep the pin in place. If not a cotter pin, then two holes (one on either side of the spring) could be drilled and a wire run through to hold the pin to the spring. Either way should prevent hinge pin creep. Third alternative that I'm not sure about, get some threaded rod the correct diameter then use really thin nuts on either side to hold it in place with a bit of Loktite to hold the nuts in place. I'd say find a bolt, but bolt heads are pretty thick and might need to be ground down. You'd need to measure to make sure the nuts have enough clearance to not interfere with the lid's operation. Simplest option, a little glue on ONE of the six fingers that the pin runs through. The other 5 will need a bit of grease so the glued finger won't break loose. If you wanted to get REALLY ambitious with it, you could drill a hole through the hinge and the pin, and use a set screw to hold them together. This would be easy to remove, if you ever needed to for some reason.
Robot and Waggs, may as well order the rest of the plastic coolant parts and get them replaced too. When I had my hose go bad, I had no other signs of problems including any signs of overheating. When I replaced them I found my degas bottle full of cracks, and the thermostat housing was destroyed inside.