D17 serial number question

.  I have been somewhat mystified when it comes to trying to determine what year or even what series  D17 tractor I have. I have seen the break down by serial number  for year and series and that certainly is straight forward enough, and unless I am reading the numbers wrong it appears that my serial number is 1212 which would be the very first year and of course series 1. But there are many unexplained differences between what my tractor has and what that early of a serial number is supposed to have. I have determined much of this by studying the parts book which shows what parts came with with certain serial number breakdowns. I know that after so many years parts could be swapped back and forth but its more then one part or one area. First there is the very old looking decals that say series IV. Then my air cleaner is the horizontal newer type, so is my dash and my power steering lines.There are others. The main questions I had was firstly on D17 models does the ID number start with D17 then the serial number? I assumed this was the case as mine shows D171212 meaning D17 serial number 1212. The other questions was in regards to the snap hitch. Was this available on all 4 series or was is discontinued on series IV? Mine has it. uploads/9178/IMG_0009_2019-05-20_00-20-48.jpeg 

Can you put up some pictures of the rest of tractor.

Hawsie,

No snap coupler hitches on a 170 or 180. Only the earlier 190/190XT's had that.

Headlights on the fenders are for Series III or IV models only.  I agree with Dr. Allis - you have a frankenstein tractor.  Sometimes I wish these things could talk to describe what kind of life they have had.