Sorry I'm so dumb, but what do you mean by "MK1" and "MK2" versions? Does this mean that MK1 = 5150 (similar to 6505) and MK2 = 5150 II (similar to 6506+) or that MK1 and MK2 simply refer to two different schematic versions/revisions of the old 5150? Thanks for the sim btw, it's very cool.