6-3-1 pairing 1-6,2-5 and 3-4 gives them equal firing order spacing. Richard Good's version has equal length primaries and secondaries which he tested against Phoenix's version where they are apparently unequal and found a big difference in his favor. The downside is Richard " cannot build it in stainless " ostensibly due to the metal's relative reluctance to bend into the tight radius required for 1 & 6 cylinders where mild steel can. He has his " ceramic " coated in (3) different temperature ranges.
I have experience with this on my trick engine with very high lift cam and triple DC