I have a '81 (according to the serial number) Mark 5 that I bought several years ago from a Fireman who was building a house with it. When he finished he sold it to me. I later sold it to a co-worker to build a house on his farm and when he was finished I bought it back.
The serial # is 111589 which according to the chart is an 81 model, however mine has the 510 package and also the the two bearing quill. I cant believe the fireman had it upgraded so i'm wondering about that serial number if it's correct or not.
Again Thanks for all the great information.