If that is not practical, then would would at least like to replace the bottom guides.
Any advice?

It looks like your original bottom guide is a match for our 23-021. However, I'm afraid they don't make a convex roller with the same housing. You could maybe try the 23-285 convex wheel assembly, but it would require you to drill holes and attach with screws. Even then I cannot guarantee it will work. We almost always recommend sticking with the hardware you have.