Have you been able to determine the year of manufacture?
Not exactly, but I believe its probably 1974-1975 range. The model number is 5VP80W0.
Does the upper wash arm lift off when loading the lower rack, or do you just rotate it out of the way as you load?
No you just rotate it out of the way, not the most convenient machine to load, but if it washes as good as some say it will be fun to use.