From time to time questions about ROPS for older tractors come up on this list. I asked our Farm Safety Specialist to give me some idea of what was available for a few common AC's. Here's what he found:
Allis Chalmers WD45 - No
Allis Chalmers D17 - Yes- net price $1910, Rops w/ canopy
Allis Chalmers D19 - Yes- net price $2696, four post ROPS
Allis Chalmers 160 - Yes- net price $1491, two post ROPS
Allis Chalmers B - No
All of these from the manufacturer Saf-T-Cab. Their phone number is 1-800-344-7491. You may also try contacting your "Allis Chalmer" dealer.
Hope that helps someone. I am sure there are others available for other models - I just asked about the ones above to help folks with the more common tractors discussed without taking too much of our Specialist's time.....!