Obviously Jim Marshall had to start somewhere and build the first marshall prototype. Does this amplifier exist? Is it in a museum? What do we know about it?
Even doing google searches which go back to around 2007, people were snagging 70's era plexis for half of what they're going for now. Seems as times get older the price and value of them continue to increase. They'd be a solid investment today for sure.
I think one of the best sounding plexis I've ever heard was a studio recording of a 1963. It just wreaks the tone of all of the popular bands and songs from that era that I grew up listening to with my grandparents. They're going for 20,000+ these days. Just surreal.
68 small box was in my view the ultimate Marshall sound. With the lower plate voltage it breaks up early and has a great feel for single note playing. The voice of Marshall was changing a lot right about this time. But I have been into the JTM45 again lately. I tend to prefer NMV for anything other than highgain.....These early amps are always going to be special to me.
The thing that has always amazed me the most is just how much people like Jim Marshall, Ken Bran, Dudley Craven, and for that matter, Leo Fender, got right from the very beginning. Those early amps are just incredible beyond description.