Jim was an ace guy - really friendly - got to meet him twice. Once at a music show in Manchester and another time when I took my old Marshall into the factory at Bletchley to have some issues fixed (the local music stores gave the usual "it'll be ready in 8 weeks" story and took 12 and still didn't fix it). He saw me with the amp and a big smile on my face, having had a factory tour, the chance to play my amp on 10 and a laugh with the tech that "designed" the JCM800 "Slash" amp, and had a quick chat. He seemed impressed that the old amp was still in such good condition and that folks were still using the older stuff. This was back in the early 90's when old retro stuff wasn't "trendy."
I sometimes regret selling the old amp head - but then again I bought it for the equivalent of about $150 and sold it for $1500 and rarely played it cause it was really too loud for home use, so I can't complain too much.
As for the 4 guys. Seth is a bit of an oddball to most folk - but he did design the humbucker. Jim's first amps, like the JTM45, were basically Fender designs with different valves - different because the American counter parts weren't commonly available in England, not because they were chosen to sound different. That said, the amps that followed were unique and were ace and are still fun to play though. It's hard to forget how loud the old 100 watt, non master volume amps were - they almost make the current generation of 120watt high gain amps seem like 50 watters and because they were non-master volume amps you HAD to crank them otherwise they'd sound like sh1t... Mmmm 'that' tone from Free's "All Right Now"... 
