Hi Sharon,
If you read the goals and process of the Magna Carta Project you will see that to have the Magna Carta template added a couple of things need to be done. First, a line must be developed from the individual to a MCS baron. Every generation must checked for accuracy. Then a second member needs to go through the line and confirm it. It is actually a lot of work.
Weis' Magna Carta Sureties and Ancestral Roots, while very good in their time, are no longer adequate for developing these lines. Too many changes have been made over the last 20 years. While it is highly likely the lines from Bassingbourne Throckmorton are still good, they will still need to be checked.