I have a John Deere RWA owners manual.
Here is a little info you might find useful about your RWA disc harrow...
The best way to find our what specific model you have is to count the total number of discs and the size of the disc. (I think some RWA's have one size in the front gangs and a bigger size in the rear....I dont know how to size those).
From pp 3 of the John Deere RWA owners manual:
RWA model . . . actual width of cut ...# of discs...size of discs
2016 7'2" 20 16"
2018 7'2" 20 18"
2020 7'2" 20 20"
2416 8'6" 24 16"
2418 8'6" 24 18"
2420 8'6" 24 20"
2816 9'10" 28 16"
2818 9'10" 28 18"
2820 9'10" 28 20"
etc
The RW model was introduced about 1955. It had a 7 1/8' blade spacing. It was superceded somewhere around 1962 by the RWA, which is pretty much the same only with 8 1/2' spacing and bearings in the gangs instead of sleeves. The RWA was produced up until 1974 when the Level-Action series of disks was introduced.
You can add a couple hundred pounds of rocks in the weight pans, 200-275# (each side) depending on the size of the disc.
Or you can add fluid in the tires and get some more weight on the disc that way, too.
Also, the cylinder you will need should be a 3"x8" or 4"x8".
I have a RW disc and the 4"x8" cylinder works just fine.
The replacement disc blades are easy to find at the local farm and home store.
I got a RW disc from a neighbor for $125. Works fine. Most folks call these RW or RWA types of discs, WHEEL DISCS.
If you want to study the RWA more, then visit this site and search for RWA and you'll find plenty of hits.
Yesterdays Tractors
The owners manual also describes the disc can be sold to customers with antifriction (ball) bearings or hard metal bearings.
Here's a picture of my RW. Does yours look similar?
enjoy.
dwight