Well, I got her rigged and on the water. Amazingly, not only does she work, but actually seems to be better balanced than the original rig.
Was only sailing for a few minutes, so can't comment too much on speed, but handling was sweet.
The mast concersion involved taking the old sleeve off and putting a thinner (2 mm wall 60mm tube) one on. This jammed on very tight.
Once rigged, she looks like it was meant to be!