I have a LeClerc Fanny counterbalance loom which uses roller bars. This is just my two cents but I have found that loom designs tend to be very specific to the manufacturer. While replacing the pulleys with rollerbars is certainly possible you may run into some additional work trying to fine tune the looms performance. Maybe try it with pulleys to see how the loom is intended to function and then if you arent happy with it, consider changing to a roller bar system. If you decide that you want to go ahead and convert the loom, you might want to contact Nina Manners at https://www.camillavalleyfarm.com/ They carry a lot of parts for repair/restoration of looms (primarily LeClerc) and Nina is very knowledgeable.
Also, I dont know if anyone has mentioned this to you, but counterbalance looms work great on balanced weave structures. With unbalanced weaves the shed is a little harder to regulate. If you want information on what Im talking about I can send you some LeClerc related information that describes it in detail, as well as some solutions. My Fanny is from the 1960s and did not come with the modification to improve the looms performance on unbalanced weaves. LeClerc does make an after-market kit to modify the loom which I went ahead and purchased and installed on my loom. New models come with the modification installed.
Thank you so much for responding Karen. I think that is a good suggestion to go ahead and try the pulleys and see how it goes. They are a bit oxidized but if I replace the old cording they would probably work. I will look into the contact you gave me and maybe she will have some good advice for me. For now, I will be happy to learn with balanced weaves but will look into the information you gave about modifying for unbalanced weaves. The heddle is in bad shape but since it is 45" I will try to clean off the rust and hopefully it will work at least to get the loom up and running. Did you have to deal with an old, not too smooth heddle?
Roller bars are, in my opinion, easier to use than pulleys. If your pullets are old and rusted, or do not move very freely, replacing them with rollers might be a good idea. A CB loom can use rollers, pulleys, or horses, and you can replace on with another easily. A particular choice might be used be a manufacturer because that is what is common in the are, or because those parts or materials are easy to find. It doesn't mean you're stuck with what the manufacter used.
When you say the heddle is in bad shape, I'm not sure what you are talking about. The heddles are the metal or string eyes that the warp threads pass through, and are held in frames or stretched between rods. You may be talking about the reed, which is a steel comb like thing held in the beater. An old, rusted, pitted reed can be cleaned, but it is usually fruitless. If you remove the rust, you are left with a rough, pitted reed that will abrade and cut warp threads. You can have the reed sand blasted, but at this point, you could have bought a new one.
What advice are you looking for regarding the sides of the castle with grooves for the shafts to rise.