I use old fence pipe for headtubes, just need to sand off the galv coating and round file the seam slightly inside to get the cups to fit. Advantage is, it is thicker wall than normal headtubes, so should be stronger for big rake builds. Not sure if pipe sizes are the same over there though.
Regarding bottom brackets, I mostly use 3 piece sets, so I cut them out of junk frames, just remember to weld them back in the right way around or your bearings will always become loose.
The reason I use the 3 piece cranks is because of the superwide tires and rims I use, a single piece crank can not be widened and still be fed through the wider bottom bracket, whereas the 3 piece can be widened no worries. (If you know what you are doing.)
Luke.