Other than the cork the rods in remarkable condition, I've tried a few short casts and roll casts in the garden with WF4 and its fine, much faster than I expected. It may well be better with a 5, I'll try one out and see how it feels.You have a good dependable Sharpes rod there, being impregnated the blank will not need to be varnished and is pretty bullet proof.
As you say 3 weight cane rods are hard to find, most of mine are 4 or 5 weights.
What i have found with cane rods is you have to find a line that fully works the rod, to get the best out of it. very often a 5 weight on a 4/5 is best.
I'm going to use it this season before I decide whether to refurbish it or not.