As you move slowly away from idle, does the misfire disappear almost immediately? Does it stumble and hesitate for just a brief moment until the revs are say 1800? Or does it stumble and hesitate for quite a while before it finally smooths out at say 1800? Does the misfire behave signficantly different between a stone cold and warmed engine?

If your testing descriptions are correct about #1 always being the only misfire at idle under all the permutations you describe then the distributor is one of the few remaining things you haven't swapped that are cylinder specific. Inspect carefully for signs of corrosion, damage or an ill fitting contact in the #1 ignition wire socket in the distibutor cap as well for excessive wear or pitting on the #1 contact stud inside the cap. Many recommend using dielectric ignition grease inside the ignition wire boots to keep moisture out. I know your distributor cap/rotor are only 4 year old Bosch, but if there's any chance you still have the old ones around it would well be worth a try to see if that changes the symptoms. A worn distributor shaft seal or bushing could be an aggravating issue for premature cap/rotor failure. Any evidence of oil leakage from under the cap at the back? inside the cap at the bottom? inside at the back behind the rotor?

Any chance your charging system or battery aren't up to snuff? Significantly weaker voltage at idle could help explain misfires. Any difference in your symptoms when moving away from idle when all loads are on (headlights, fan hi, 4-way flash, de-fog,etc.) compared to all loads off?

Before you started moving things around, did you read and compare all four spark plug tips? Differences in colour, fouling and wetness can tell you a lot when just one cylinder is involved. Any chance you have unexplained coolant loss and #1 plug is notably cleaner?

If you hadn't described all the testing you did, my first guess would have been bad ignition wires, like a weak contact at the #1 spark plug boot. Sometimes simply using pliers on the outside of the boot to pinch in the contact collar so it will fit tighter on the spark plug can help with such matters.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now