Re: whats horizontal input??
It's actually the other way around. It refers to 2 input Marshalls, mostly JCM 800's. The one's with inputs layed out vertically meant that there was actual wires leading to the preamp of the circuitboard, which translates into punchier, better tone. The horizontal input Marshalls, like the late 80's ones, were produced a bit cheaper, since the input jacks were mounted right on the board, sending the signal through small tracers on the board. These kind of inputs also tend to break easier, if you accidentally step on the cord.
They stopped using flying leads on Marshalls inbetween 83 and 85, I believe.
That's why sellers of vintage Marshalls boast about Point to Point construction, pre 73, and vertical inputs from mid 70's to 84, or so. Every few years, Marshall tended to cheapen their construction methods to cut cost. The last one was when the JCM 2000's went from hardwired Drake transformers, over to cheaper Axiom trannies with unpluggable wiring harnesses. Easier to service, but lesser quality transformers.