On Mar 5, 7:02 pm, "Viewer" wrote:

snip

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.

You can find SawZall blades with tungsten carbide edges at amazon.com.
While not as hard as diamond, for the limited corner cuts they should
do just fine. HTH

Joe