Wow, another lawyer with a JD5105. It must be the lawyer's tractor!
Have you considered a disk plow? Monroe Tufline makes 3-disc disc plows that would be suitable:
Agriculture TDP Disc Plows - Monroe Tufline
Or, maybe consider a chisel plow:
Agriculture Chisel Plows - Monroe Tufline
(or several other companies, such as Baltic)
As noted, moldboard plows are rapidly disappearing from big ag. I think most farmers who still do conventional tillage are using offset discs, but those don't generally come in a size suitable for a 5105. The disc plow above is very similar and would probably be, in 3-disc configuration, the biggest plow you could buy new and realistically pull.