Jim,

Just use the best tool available, and consider the value of your time.

Myself I would bandsaw the disks on my vertical bandsaw. Your method
of "gas axe and grind" sounds doable if you can burn reasonably well.

As you say, sabre saw sounds painful.

Can you fit your gas axe to a crude circle cutting attachment
jury-rigged?

One other method would be to phone metal fabricators in your area and
check their price for disk burning from your material.

Also a scrap yard may have disks from boiler manufacturer's scrap pile.

As a final resort you could cut out the disks by drilling.........I
used to do this before I got my band saw and modified it for metal
cutting. I used 3/16 dia. drills because I had a lot of them.

Trust this is of some help.

Wolfgang