Having done plenty of land surveying in my life, these tripods look awfuly similar to surveyor's tripods (except those use a 5/8" connection).... they could be modified, of course.
Yes, they are very heavy (how much, I'm not sure). But they are also very sturdy. They're meant to hold precision optical surveying equipment that measures angles and distances from a fixed point, so you don't want the tripod moving around at all. I've used them in all kinds of weather (except the extreme) without problems, too. I wouldn't want to walk too far with these strapped to my shoulder, although it's bearable with a shoulder strap.
These are overkill for 4x5. More suitable for ULFers, in my opinion.
Having said that, my old school, no-name wooden tripod is pretty dang light and carries my 4x5 and 8x10 without a problem, even light wind.