Mark Curtis' model is essentially comprised of Hoogsteen pairings - and allows for two double helices to intercalate as shown on his website and in this video.
"For completeness of the present discussion, the structure of the DNA fiber at 92 per cent relative humidity is summarized. A detailed analysis of the model will be presented elsewhere. It consists of two Hoogsteen base-paired double helices with a pitch of 67.2 A each, held together by partial intercalation. The base-pair separation for one double helix is 6.4 A so that the effective base-pair separation for the four stranded structure is 3.2 A."
"Today on the show we’ve got a conversation with Dr. Zoё Waller, a researcher at UCL, who specializes in the myriad ways that alternative DNA structures affect biological processes.
Today’s guest - and this entire line of investigation concerning alternative structures of DNA - comes to us as a recommendation from one of our patrons, Sean Kettle. Shout out and a big thank you to Sean for connecting us and making today’s conversation possible."