Yeah, I would say that you probably have a performance cam in there. Probably the S&S 600 or something comparable. The late closing intake valve causes the big dip in the midrange, but it really makes power in the high rpms.
It's true the 107's didn't have to deal with epa emissions, but all vehicles have had to deal with noise regulations for a long time. That's why most stock exhausts aren't very good for making power, although I've heard the Kerker on the pre-05's was a decent exhaust. Performance cams can also increase noise levels. I'm not sure what the reasoning was, but some 107's came with the 600, and others came with the 520. The 520 was really bad, even worse than the epa cams in the 117's.
I don't know, but they should be easy to tell apart. The 600 should start really pulling above 4k rpms. The 520 has an early closing intake valve and nearly no overlap. It should have decent bottom end punch, but it shouldn't have much pull in the higher rpms.
520 cam may have been California bikes? But could had a surplus and just shipped where ever bikes were needed? Just a thought or guess as to way there were different cams.
The 107 were always known for having the 600 cam along with the performance enhancers that made it work. This is the first time I have ever read about using the 520 cam in a Big Dog 107.
..yeah..... what he said ^^^