Late to the thread, it seems most questions are answered.
This is a good site for deciphering those model codes
FORD CODES and SERIAL NUMBERS
And yes, it indicates a gasser. So one can only assume it had an engine swap somewhere along the way.
Yes its a 755 backhoe attachment, and thats the 740 loader attachment too. So if you need to look up parts on newhollands website. The hydraulics are indeed separate from the transmission, and the loader/backhoe frame is actually tube steel and is the oil reservoir.
Not sure on the trans or how different it is than a 5500. I had a 5500 with the TC trans and the suction line for the torque converter charge was on the bottom of the trans. A 90° steel fitting. Any condensation would settle to the bottom then freeze in the winter. Had to crawl under there with a propane torch several times in the winter when I needed it.
When you stopped on the road and saw steam at the shift boot.....that was probably just getting it up to operating temp and cooking the water out if the oil. Dad had a 4500, but his was not the TC trans so I have no idea about that.
IF you think this 4500 is already a little bigger than you wanted, be thankful it wasnt actually a 755. Otherwise you'd have a 18000 pound monster instead of the 10,000-11,000# machine you now have. My 5500 was a predecessor to the 755.
Here is a side by side shot of a 4500 and a 5500
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