5B3293/4 were the earliest 6.75 " pitch links at 3.88" high new.
Followed by:
5H8679/80 @ 3.88"
1M1431/2 @ 3.91"
2M8863/4 @ 3.91"
7M8863/4 @ 3.91"
Latest numbers being 2S5959/60 @ 4.0" (link assy # 2S7579)
Thank you for posting the link numbers.
My local Cat Dealer here in Australia quoted me around $US2,400 per side for new RD6 chains this year, he said they had them in stock in the USA, he also said it would cost around $US1,800 per side for them to turn the pins and bushes on my old chains if I removed the grousers first.
regards
Mike