This is a very popular size for my industry (bikes) for full frame layout. I’ve got 3 of them, but they have been tough to find in decent condition and that size. My advice: used cast iron plates are very nearly always dinged, gouged, have been hammered on, welded on and are generally beat up. They started as inspection plates, and then if not calibrated and kept up, then they became a bench plate, then a layout table, then a heavy work bench. Remember with used CI plates that no matter how flat they appear to be, you still need to get them calibrated so you have the data of a known reference to your work/Fixturing. What are your required tolerances for your plate?
If you need to use magnets for fixturing, then keep on looking. If not, consider granite. They are often in much better used shape, and can be reconditioned and calibrated by firms who travel to your shop rather than you taking the plate somewhere. For fixturing, any granite shop can jet the holes for you wherever you want. I’d recommend getting the holes drilled oversized and then you can insert and machine to your specs.
My apologies if you already know all this and have considered it, but again since it’s a desirable size for my work I and many others have been down this same path.
