Adding 2 new 6v: what config?

My old 6V GC2 in series are ok, but 3-4 years old. But I'm thinking about adding two new ones, same brand, just new.

What's the best way to do it?

A) Both new GC2s in a new 12V series, placed in parallel with the old GC2s in the old 12V series?

B) Or the other way: mix one old with one new in each 12V series.

They will all be permanently cabled and charged together.

I do occasionally check the Sp Gr. Here's the old batteries:
1.275
1.265
1.262
1.280
1.280
1.275,
and equalize every 3-6 months.