Hi
The 55 Gold Star would have had 5 friction plates on the 500 or 4 on the 350, the amount of plates fitted did vary over the years so it is not critical.
The six spring clutch fitted is very heavy in action, if you need to buy a lot of parts for it it may be worth looking at fitting the later four spring Triumph clutch which is much lighter in action and fits straight on, this was fitted by BSA to the later "B" and "A" series bikes.