I have an old cave diving manual (I'll have to look but it is I think 1973 vintage) that outlines the clorox bottle approach and has a few other methods as well - but they are all clearly referenced as ancient cave diving "history" and the horsecollar BC is the clear standard of the day. (The irony here is that the Scubapro Buoyancy Control Pack came along shortly after (1975 or 1976) and ushered in the whole wing era.) (The further irony here is that the then new jacket BC's were also very popular as a place to start with for modifications to create the early DIY sidemount systems of the era.)
I do know that horsecollars with thin collars around the back of the neck were more highly prized by cave divers of the day due to the reduced trim issues otherwise caused by too much air migrating there.
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The same manual also addresses cheater bars and pig tails as means to connect two ingle tanks and discusses the relative merits of single outlet manifolds, independent doubles, cheater bars/pig tails, Benjamin conversions, and the not yet created but envisioned "ideal" manifold - a modern isolator manifold.
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Speaking of blasts from the past, I saw some 1" button gauges at Beneath the Sea that, unlike most button gauges that just have a small hole in their base, were milled to accept an HP spool, so you could conceivably put them on the end of a high pressure hose like a mini Seaview gauge.
