Im no expert but I've spent a lot of time on both boats. The HT weighs maybe 2/3rds(or less) of the 20, I think the rig is taller too. My guess is that the ht mast would snap like a twig. It is wayyyy lighter than the 20 mast. Is your 20 mast one of the old carbon ones or a new aluminum one?
The I20 mast was very old carbon technology and far heavier than it was robust. Over what it was tasked with originally, you're really only asking the HT mast to carry a jib and cart around another 125 lbs of boat. It would probably be more sensitive to mistakes but I bet it would survive.
