Typically:
Everything except 338LM is #6
338LM is #8
Is it new? If not, the previous statements may not hold true. The previous owner may have had drilled & tapped for #8.
What about having the 6-48 holes opened-up to 8-40? I don't know what scope you're mounting (read how heavy the scope is), but while the Seekins base has an integrated recoil lug the added strength that 8-40s provide is always welcome.