I think girdling is very common for lychee production, don't see why it wouldn't work potentially
for the mac. I would always worry about it negatively affecting my tree.
If you got a nut, that says the ensuing years it should gradually increase flowering/production
from here. The hurricanes might have changed it for this year though. Have you had a growth
flush yet this spring? Once you do, within a few weeks perhaps you'll see some flowers. They,
while not inconspicuous, aren't real visible until the flowers are opened. I've done some research,
and its a slow increasing process of flower production the first few years. I also read where their flowers aren't
found to be that desirable by bees, so other flowers will generally get more attention. Manual pollination
might be helpful. I'm hoping to research mac nut crackers in a year or so!

Gary