I think rick meant on the simulated failed engine. Instructor pilots simulate a feathered engine by "zero thrust". FAA would like to have all simulated failures below 3000 AGL done by pulling the throttle. After the student performs the engine out procedure up to feathering the appropriate engine he says "feather left" or "feather right" the power is brought back up on the throttle just to the point that the RPM matches the operating engine.
This is approximately where the prop is just pulling itself through the air, simulating feathering.
As I said, good job. The drag on a windmilling engine is quite significant and with a lesser light twin than the 310 or a heavy load it still may not have flown. I like your attitude, all experienced pilots have had a few times when they realized they were just plain lucky.
There is no requirement to do a SE approach with a windmilling prop. Many light twins will barely fly with one feathered. As I said in an earlier post the reason for the prop not feathering should be found and fixed.
Why did the prop not feather?
A twin has props set up to "fail safe", in other words a combination of centrifugal twisting moment, spring or counterweight force should drive it towards feather. A single engine plane's prop drives it toward flat in the event of loss of oil pressure so you have some power. I would check to make sure that the gov has full travel and if it does is it ok? Sludged up prop or crankshaft?
Good job flying, when teaching in the 310 we used to do an L/D demo where you set up at best L/D speed (120 mph I think) in stable level flight and then introduce drag producers. After each drag producer you would descend to maintain 120 mph and note the VSI. Full flaps were the worst, 1200 fpm down or so, a windmilling engine was second and produced about 800 fpm down.
I fly a Rockwell Turbo Commander. The door is directly in front of the left prop and is locked at all times (by a swtch in the overhead panel) tthat the prop is spinning. Even if my boss is saying to unlock it so he can get going, I tell him "no". I also do maintenance checks on the plane with the engines running and have to constantly remind myself not to walk thru the prop arc as you do hundreds of times with the engines shut down. She deserves the insurance and I do feel sympathy for the pilot as well.