The bike is a Sussex. It's a fairly new bike, but a bike that's been in production for probably over ten years. It's put together with parts that seem dated and frequently odd. No brand name is on the crank.
Well, I've thought this over. The crank really is held in place by being jammed on the tapered axle ends. The bolt does nothing but prevent the crank from slipping off the tapered ends. I would "think" that torque isn't all that important. It has just to be enough for the bolt not coming loose. And that's why it's so odd that the original bolt is a high tensile strength (12.9) bolt. It's just unnecessary, but going by the rules, every bolt is made with a proper torque spec in mind. So I went to the bike shop and checked regular crank bolts, which are M8x1.0 Allen flange bolts of unknown grade. I also saw some M8 outer hex (14mm head) flange bolts and plain old hex keys with a loose washer.
Nobody can tell me the proper spec. The bike mechanic torques them "good'n tight" with his calibrated elbow. I'm now using a regular, modern M8 Hex flange bolt with blue threadlocker and use 35 Nm (26 ft-lbs). To me, 50 ft-lbs (68 Nm) seems way too much for an M8, regardless of grade.
The bolt in the front is the original bolt. The bolt in the background has the loose washer, which in my opinion is preferable. The bolt on the right is what many current bikes use. I ended up getting that type, but with an integrated plastic cover, mostly because I'd rather carry a 8 mm Allen than an 8 mm hex socket. It also looks pretty.
You can see that bolt installed in the picture below:
I'll find out if it comes loose...