Wow... differing opinions!
I think the JD is identical to the NH machine. They have almost the same lift design -- both are exactly scissors-lift models, both have a low engine hood, both have interior-operated boom locks, both have two low-mounted boom stops, both have damned large tires, both have direct-drive, both have the same size chains, both have handles on the boom, both have four hydraulic cylinders, both tout their stability, both have operators saying they're great because they're more stable... the list goes on. I know they're not nearly the same machine, but the JD looks (simply from its frame design) like the NH. I'm not displeased with this -- JD has gone far in SSL production -- it's just that I'm not surprised because NH made the JD SSL for a long, long time. (As you mentioned -- the 8875 down to the 3375 were all rebranded and re-engined NHs.)
Let us know if you come up with more 300 series specs or info
Xing