I did check Walthers, the problem is, very few companies (except those I listed, and even those aren't 100%) list the dimensions that are critical in at least this application, as far as I could find...the "height" of the nut is the main one that I don't find listed. Based on some pictures I've seen, some of the nuts are nearly as wide as they are tall, which in reality may be correct. Based on how HL cast the ones though, they should be more than twice as wide as tall.

In Walthers case, some of the ones linked (for instance) show 1.25" for O Guage. But still need to know what the real size is you are trying to replicate. Apparently "G" is the largest train size, but due to the real deals immense size, G is 1/22.

Just can't get my hands on a real StuG to measure with my dial calipers!

Cone head bolts? Are those the ones on the rear shield that is just above the exhaust?