Silas JEFFERSON is mentioned in same breath with McNACS. I'm confident Alec is the son of Wallace McNAC. At the very least they appear to have been political allies. The kinship link may not be far away.
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Paper: Dallas Morning News Historical Archive
Date: 1901-02-27
Headline: Rounding up Snake Indians; Marshal Bennett Returns to Muskogee with a Big Bunch.

Special to The News.

Muskogee, I. T., Feb. 26.—The following is a list of the prisoners captured by United States Marshal and his deputies in their last round-up of members of the Snake band; Jim Gordon, Gabriel Foster, John Deere, Pompey Phillilps, Judge: Silas Jefferson, Town Chief: Alec McNac, lawyer; Aaron McNac, Barney Sewell, Pompey Perryman and Court Hennery, lighthorsemen; Katcha Marthia, alias John Tiger. Councilmen: Edward Gooden. Town Chief: Sam Bruner, Town Chief: Oches Harjo, Town Chief: Hulputta Fixico. Councilman: Tulwe Harjochee, Councilman: Yaha Emerthlogee and Talmarsee., lighthorsemen; Wotka Warhola, alias Barney Marshal, Town Chief: Parkes Micco, alias George Hicks, warrior: Joe Grayson, lighthorseman; Rolly Taylor, Councilman. Judge Sanson and his traveling Commissioners’ Court which accompanied Marshal Bennett have returned to this place. This was probably the last round-up which will be made for some time.

Preston