Yay. After another concerted attempt, the pin is out. I had tried moving the bucket to relieve the pressure on the pin and had no luck. This time, following radioman's suggestion above, I tried lowering the stabilisers. Left side, then right side.... no luck. Then, I put pressure on both left and right, just a touch, and out it came. After removing the back hoe, I could see that the side with the offending pin had a lot of Kubota orange left on the inside of the plate... the other side had only surface rust - so corrosion is your friend (at least in this case). I've used Emery paper to remove the paint - I'll know next time if it helped. Thanks again.