I've only ever heard of 2, close chambered heads on a /6. RRR has one, Doug Dutra has the other.
I have both peanut heads and a drool tube head here off of engines. No difference in combustion chambers on the ones I have, among them. All of mine are 74 and newer. 74 was last year for drool tube heads
There's an article on the /6 site about this, there was a modification on heads' combustion chambers after 1968 vs those before, and the after 68 heads were deemed better/// but when they went to the peanut heads, that part didn't change.
I don't think there's a difference in spark plug angle anywhere along the lines.
One BIG difference between drool tube and peanut heads is that with a peanut head you eliminate 6 certain oil leaks, those being around each drool tube.my last build was a 74 225, and I put a77 or 78 peanut head onto it for that reason. I still have that original '74 head here in the garage.
Also back when my dad had his 82 gran fury with it's /6 and he ended up with a cracked head, I put on a 60s head to get him going again using what I had laying around. Valve cover was different 81 and newer vs any /6 before then and I had to drill out the last hole in the rocker shaft but that was it. Direct swap/bolt on, besides that.
I see others chimed in while I was, and beat me to most of what I said here.
