Hey, daman. I am only about 30 miles east of the old Romeo tractor plant and i think they are making engines there now a days ??
They've been making the modular V-8, 4.6 litre, for at least 15 years. I remember driving to the Yates Cider Mill in October most years, and the Romeo plant was in the neighborhood.
I don't know what pre-dated the 5500, but it went to my 5550, '74 was the 750, then the 755, and I don't know what NH called the big mothers..
My 5550 was 17,000 pounds, then add about 3,000 pounds for the ROPS, dig-more, and the thumb. All that weight planted it pretty good so the hydraulics didn't just slide the hoe around.
It needed a bigger hydraulic pump to run the big cylinders, they got that in the 750 with a turbo and about 105 hp. You could do some serious damage with that one, my slower unit was perfect for someone that didn't have thousands of hours on the machine.