Thanks for the replies so far. It does appear doable and it looks like
one option for a blade is the Felker GD-10 blade (available in 7"
size) for dry applications on granite. I agree that a squeeze bottle
of water would be a good idea for lubrication, dust control and heat
removal.

I had originally intended to do the cutting in place from the top side
(to minimize potentially cracking the slab, but now I am wondering how
to finish the cuts in the corners (so I don't "overcut" the top in
order to completely cut the bottom). I am thinking that perhaps a
diamond blade is available for a sawzall or jigsaw, as I will only be
cutting in the corners a short distance and at a reduced thickness.

Hmm.

That's why I appreciate all of the comments here.