I believe that the mid-1980's Hunter 31 was one of the first Hunters to use a B&R
rig, which was characterized by swept back spreaders and an extra set of diagonals in each panel. This was a pretty unique
rig that reduces the loads on the shrouds, allows precisely controlled mast bend and provides spar rigidity without forward lowers and allows a smaller/lighter
rig. By comparason the Pearson spar is pretty primitive and probably not suitable no matter what you do to it. Regretably the B&R
rig is not one that would be easy to buy at just any spar shop.
I would suggest a few options:
First, Hunter actually has very good customer support, so you may approach them and get a price.
They used to contract out their spars so you might ask if they can refer ypu directly to their spar maker.
Regretably, a new
rig may end up costing more than the whole boat is worth, which is not all that unusual for an older, low value boat.
Another option is that the Hunter 31 was a very high production number boat and many were around the Gulf of Mexico, so you may be able to track down a spar from a boat lost in one of the hurricanes. You will need to inspect the new mast carefully, as any
rig that has been on a boat that was sunk has potentially been subjected to loads beyond its original design intent.
Good luck
Jeff