It's 242 cubes inches of inline obsolescence. I'd love to answer the second part of that but I'm not exactly sure, probably 2800-3600rpm though. I'd just swapped the cluster to one with a tach and then mangled a link mount due to running out of talent, so I haven't driven it on the street for the last week. Once I fix it I'll collect some data while driving by paying attention to the tach. Between a combination of horrible aerodynamics and massive rolling resistance the engine is always working fairly hard above about 30mph. Hence it winds up sitting somewhere in the mid-RPM range and just droning. You are correct that it is a very irritable noise/vibration and slowly drives you crazy.
I actually decided to order a high-flow cat to try splicing in first. Assuming it fits. I may have to cut the floor to get adequate space, but so be it. I looked at it more while cycling the suspension and I don't think I can actually run the pipe out the back, there just isn't space past the leaf spring shackle, but I can turn it a bit and dump it, which might help too as it should direct the pressure pulses away from the floor/body. I don't know.
I did spend a whole day (6 hours of actual driving) in it on the trail and it's totally not annoying as long as you're doing technical stuff. It's going to be unbearable for snow wheeling though, as that normally involves holding 50-75% throttle for hours on end. Nobody took any usable video of me (bunch of boomers can't figure out how to do much more than make a phone call with a smart phone, what can I say), but I do have terrible knock-off GoPro footage where you can't actually hear my exhaust, but hey, watch it if you want, or don't.