I’m fairly certain this is not the cause of your issue, but, changing the body mounts made a tremendous difference in how much vibration made it into the cabin.
My vibration was in the rear differential. I had some old damage to one of the leaf spring hangers and over time it allowed the rear axle to walk back and forth which destroyed the pinion bearings. The first thing I changed was the body mounts. Didn’t fix it, however, the difference was very noticeable.
Fixing the leaf spring hanger and replacing the suspension made a big improvement, but ultimately I had to install new differentials and the issue completely resolved itself.