Always six bolts from factory or?

I have a new replacement pump on mine that is also 6 bolts. It's a brand new pump but it's from around 1981 if I'm reading the little tag on it. I dunno if deleting the 6th bolt was a year thing on the aftermarket pumps or what.
I found my replacement pump on eBay.
On another note, I've got dutra's book and have been around the other /6 site for years.
My new pump is cast iron, and it has OE sized 5/8 thick rotors in the pump. Most regular (non hi volume) replacement ones are 7/8 thick. I took it apart and deburred everything I could see. It had a few pretty good casting "boogers" that I feel better knowing they're not there anymore.