Slab saw voltage

I personally prefer most my tools to be 120V, more universal, the only 220V in my shop is for the welder and compressor. If I was cutting for a living, I would probably convert to 220V on the saws, but I don't do enough cutting to worry about the price difference in KW. JMO.

I say absolutely do it, 220V motors that run 1700-1800 RPM generally are priced better than the 110V equivalent.
Even though, as rockbrain said, the draw is the same, running 220 pulls from both legs and the way electric meters work a more balanced power draw does show up as less consumption in a lot of cases. Single phase won't show as much difference as 3 phase, but it all adds up over time. If you want to get into a major study you can look at power factor of the motor, power factor correction when necessary, and things like whether your utility uses time of use pricing and so on.
With the 220V I would add a relay of some sort so you can use a standard switch, or even a starter button plus shut off switch like HP has to avoid the saw starting with the lid open. If you find any of my recent saw build threads I think you will see my method of wiring to include a switched box with receptacle so motors just plug into the box, makes it easy when changing motors, no crawling on the floor disconnecting wires from inaccessible panels on the back of a heavy motor.

Looks good, about the same vintage as my FranTom 18 with the grease pot on the clamping dog. The sheetmetal legs on those is a concern, seen plenty of bent ones. My saw rides around on a plywood cart with casters that came with it, and it had 2x2 boards screwed to the legs as stiffeners. I want to add the angle iron horizontally between the legs to secure them and act as a base for casters and a shelf for a kitty litter tub for the slabs. The motor mount stiffens things enough at the rear to not necessarily need the angle there but I will probably go ahead with it, plenty of steel on hand. I would definitely treat that rust with a converter or naval jelly, grind it all off, and coat with the rustoleum rust paint or POR15 to stop it, looks like it must have been exposed to the NE salted slush somehow or just general marine air.
Mind the jaws on that, the HP and FranTom jaw design can bind in a way that the rock seems clamped, then slips out on you during cutting. I keep them parallel with my Jaw jacks, basically 1/2-13 bolts with coupler nuts to adjust, but many people just use an assortment of wood blocks. And a little tappy-tappy when tightening also goes a long ways to secure them, especially the difficult round rocks. I have a video showing the jaw jack and the use of a small hammer to ensure the rock is clamped. I also glue most cut rocks to boards for cutting, but that's a separate thread.