SOunds like a fuel isse. I'd take the distributor cap off and dry it out with a paper towel, but it sounds more like something is amiss with the carbs. Maybe the needle valves are stuck shut. Or the fuel bowls have a little frozen water in them. Or the fuel pump isn't working. Take off the air cleaners, squirt a little starting fluid down each throat, and see if it fires up. When running, see if you can see gas at both jets.

A timing issue probably didn't happen while it was sitting, and it wouldn't idle well if that was the case either. It's probably just not getting enough gas to do more than idle, the backfires sound like lean backfires to me. Also check the oil in the Su dampers. If those go dry, the car gets really lean and cranky when the pedal goes down. If that's the case, though, it should run well if you open the throettle really slowly. If the fuel pump is barely working, though, it will falter regardless as the motor outpaces the fuel supply.
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'63 PV544 rat rod, '93 Classic 245 + turbo