Tom,
To get an idea about how tall mast you will need, I have now sketched up a JR for that vessel. That sail is actually a down-scaled version of the sail I have on my own boat, Ingeborg.
If that Com-Pac were mine, I guess I would look for an aluminium tube with Ø125mm (5”) and with a wall thickness of about 4mm.
The boom has been drawn in with enough clearance for a tabernacle - just. However, if I were to lower the mast only twice a year, I would consider making an A-frame crane from two 6m poles.
Have a look.
Arne
PS: The LAP (above deck level) is 8.26m.

(Details in Arne's sketches, section 8, photo 33)