Beautiful work, Ptree.  It's got to be really neat to have an anvil like that!

Zip wheel on a 4 1/2" grinder comes to mind. If you are going to do much metal work, a 4 1/2" grinder is almost a necessity.   Just grind most of the way thru all the way around. Abrasive chop saw would be a 2nd thought if you have one, that or an OA torch. Other options, sawzall, portaband, abrasive wheel in a circular saw, push comes to shove metal blade in a jig saw.

If you forge your hot cut 1st, you could then heat and hot cut the rest.

DSW beat me to it, Harbor Freight had 4 1/2 in Grinders for around $10 and multipacks of cutoff wheels.  Are they DeWalt or Milwaukee?  Of course not, but they get the Job Done