One thing to note is that the A-frame is designed so that the noose that goes around the mast is positioned very close to the mast's center of gravity when the noose is a foot below the top of the frame. Since your mast is about 3 feet shorter, you'll want to keep the noose about 1.5 feet lower.
As for using pipe instead of wood, that's a pretty good idea. We have a lumber yard / hardware store right by the marina, and wood seems a bit easier to work with, otherwise I'd go with pipe. I'd still like mine to be disassemblable of course.
I'd love to come and help out with your unstepping, but, continents being what they are...
s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27