JW,
If you think your grandfather was a Sizemore you should join our Sizemore project and take the Y-DNA test to see if you match any of our present groups of male participants. You might also want to consider taking the autosomal Family Finder test too.
https://www.familytreedna.com/group-join.aspx?Group=SizemoreI suggest selecting the Combined Tests of Family Finder + Y-DNA12 to start with. You can always upgrade the Y-DNA later if need be.
Joy
joyk@sc.rr.com