In addition to the 1RQ and the #16 with the quill option, there was also the 2RQ and the monstrous 3RQ. I have a 2RQ and it tips the scales at around 4,100#. The 3RQ is somewhere north of 6,000#. These machines are capable of generating several pounds of chips per minute. My 2RQ only has 5hp on the main spindle, but with 50 taper tooling, I've used a 6" diameter multi-carbide insert face mill to hog 1/4" off the thickness of a 6" wide piece of 1018 at 2-3" per second. Virtually no chatter.
If you ever have the chance to see one, the 5R (a non-quill machine) is probably the largest production mill that was ever produced. 20hp spindle with either 50 or 60 taper tooling (yes, there is such a thing as 60 taper - drawbar is either 1-1/8 or 1-1/4" diameter vs. the 1" of the 50) with up to a 96" table and topping out well over 20,000#. There were probably fewer than fifty of these beasts made. I had a chance to buy one with two pallet loads of tooling five years ago for $2k. Been kicking myself ever since.