I'm not really experienced with anything that old (oldest machine I've worked on was early 90s) but if the switch is connected directly to mains with only a fuse (if that) in between, your switch only needs to be rated for the line voltage in your area (but go a little higher, to be safe and you'll find more parts rated 125VAC or 240VAC than 110 or 230). Amperage is actually more important to get right! Make sure the switch's maximum current (Amps) is GREATER than the fuse it is in-line with, or you might start a fire.