Confusing Royalty Deed. Need help figuring acres owned

I have a “Royalty Deed” for Simpson County Mississippi, recorded in 1958 for “50 acres under a 340-acre tract”. I have a Division Order dated in 1963 for a 40 acre plot covered by this Royalty Deed. The well is still producing. I do not have a copy of the lease covering this holding.

My grandfather was a part of a group of men who purchased mineral acres. They referred to themselves as the “Cubs”. Some of the Cubs were land men and purchased mineral interests in their names and would then sell those interests to members of the Cubs who were interested in purchasing. On this Royalty Deed the purchaser sold 7/8 of his mineral interests, retaining 1/8 for himself. (There are 8 owners, each with the same 1/8 interest).

Also, the deed has what I refer to as a stipulation. It reads “ 7/8th of 50/2720 of whole of any oil, gas or other minerals, except sulphur, on and under and to be produced from said lands; delivery of said royalties to be made to the purchasers herein in the same manner as is provided for delivery of royalties by any present or future mineral lease affecting said lands:” The stipulation goes on to discuss sulphur but it is not applicable because the well produces oil.

The original Division Order reflects each of the 8 Cubs owning a decimal interest of .00205323. The property is SW/4 SW/4. The division order doesn’t state acreages, but I found plot picture on-line and it states it is a standard 40 acre plot. How do I calculate the number of acres my grandfather owned in the well plot? By my calculations he owned: 1/8 of 50 acres = 6.25 acres in the WHOLE tract covered by the deed, but I am not certain how to calculate how many acres he owned in the 40 acre well plot. It can’t be much! Does the "stipulation" affect the calculations?

In the end, I was hopeful I could back out the fraction used on the lease. I have all the original deeds for royalties owned by my grandfather, but often am missing the old lease agreements. Presently my grandfather’s holdings have been transferred to 4 family members. We are attempting to put all into one holding unit. We would like to have clear tracks. Is there a site on line where you can search for old lease agreements?

If you are getting royalties, couldn't you ask for a copy of the lease? Say if you challenged their calculation & said that you were entitled to a different percentage of royalties?

Also, find out the net mineral acres owned. I was surprised that it is considerably less than the 70 acres I own.