I am not sure (didn't research it first) but, maybe, Toyo standards are "multi-purpose". You could use one of the 45D standards as an intermediate standard, two bellows... and have hella-long bellows extension!
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Definitely possible, but with the 45D the bellows are screwed to the standards and meant to be not "user replaceable". Nuts to that, I bought a bag-bellows for a 45G, took the endcaps off, and screwed it into the standards of my 45D. Worked perfectly until I bought a 45G and put the bag bellows back onto its frame to use on the 45G.
Also, if you've got a 45D and need more extension, just grab an extra standard & bellows from a 45G and put it on the front (or back) of the regular 45D, that works without ripping any glue or unscrewing anything. I've got 3 standards on my 45G, with 2 bellows I can do nice close-ups with my 600mm Apo-Tessar and 465mm Apo Ronar.
They do have so-called 'intermediate standards' which basically join 2 bellows together, but front/rear standards are easier to come by used these days (I bought a 45G front/rear standard from B+H used for $30 or something).
Of course now I've got a 45G I don't need the 45D anymore.
Speaking of which, if anyone missed out on the parts in this thread (sorry for hijacking), I'm parting out my old 45D similarly, when I get around to it after exams...
edit: Actually, now that I think about it, I do remember doing something similar. I had the front-standard and bellows of my old 45D attached, the rear of the bellows I put a 45G bellows frame on it. Then when I needed more reach on the 45G, I attached this extra bellows+standard to the front. But yeah, ditched doing that when I got my spare 45G frame.