Wow, that is a beautiful planer! Quite wonderful it lasted in good shape all that time, too.
I put off planing the table on mine for years, always imagining that I would not do it until there was time and equipment (overhead hoist/rigging) to scrape the ways first.
Then I came to consider that even if wherewithal to scrape the ways accrued, it would still be most prudent to plane the top of the table first, to relieve accumulated stresses in the casting. Old books are full of stories about planer tables humping up in the middle. This is slightlly because the ends wear first, but apparently it was not uncommon for a well used planer table to rise up to where there was clearance off the ways, in some instances. This is from all the peining of the surface, and the undersides of the T-slots, from dings and such, but mostly just from constant clamping and hammering of furniture, pins, and such as a normal course of work. Jim Christie once linked me to a book where they where raising the table on cribbing and bashing down on the middle with sledge hammers against wood blocks prior to resetting it and taking a skim cut. I have read several similar suggestions and accounts.
Like yours, my planer gets used a lot for regular work. While I generally set things up on parallels and jacks to effect a level surface when needed, it became a major inconvenience for typical work. Last year I finally planed the surface, with no regrets. Unlike yours, IIRC mine was humped up in the middle perhaps .030" or so. It is unusual that the corners would be high.
Your belts look about as wide as mine (1-1/4"?) which on mine transmits 3HP. (Planer is rated in the catalog for 5 or 7 HP. Have not figured out how the belts would manage that, though) I have no doubt yours will drive a sharp 3/4" or even 1" wide spring facing tool at the typical .001" +/- depth for a finish cut. You may want to do prep work with a deeper cut and narrower step over depending on tool material. I would not use carbide. Especially without a tool lifter. Though you can stand and manually lift it. John O sent me a nice care package of some P & W tool bits, roughly equivalent to CPM M4 which is my hands down favorite planer tool material.
The biggest holder here takes 3/4" square bits, and the step-over on the planer is "comfortable" around 3/4", too. I sharpened a 3/4" bit square across the end with a slight hollow grind, on the surface grinder. (Hold bit vertical in vise on the magnet, run table in and out under the wheel to put a hollow ground straight edge on, with just a few degrees clearance). I dubbed the corners of the tool to slight rounded bevels with an india hand stone, and honed the edge sharp enough to shave hairs on my arm, on a white hard arkansas stone. These are tools for a different job, but same stone.
This was put in a holder that positions the bit behind the clapper pivot point.
Then I carefully set the tool to the bed, observing with a strong light behind it. Another option is to set the tool as close as possible to the bed, then lift the clapper and lower the slide just enough so the tool sets back down at the back-clearance angle. Put a piece of 400 or 600 grit SiO paper under the tool, and slide it out frontwards, honing the tool to the bed. I did not do this, but it can remove the last sideways discrepancy, and put the faintest unavoidable touch of round on the tool which is considered desirable by some.
I set the step over at 5/8" of an inch, made several light roughing passes, re-honed the bit, and made a couple finish passes of around .001", and then one of less than that and called it done. It is worth making sure everything in the stepover mechanism and clutch(s) is working perfectly, for a uniform appearance of the tool marks.
Photographs of tool marks often look deeper than they are, these will tickle a .0001 indicator, but not much.
Overall views of the table after planing
Close ups of the finish:
A hook tool will do even better, but if the edge breaks down it will likely fail in a way that requires grinding out of the machine and resetting. Instead of honing in place.
I put an airlifter on my planer a few years ago. Let the roughing cuts inform the set up for your finish cuts, but it would not be out of line to put a lever in the clapper and manually lift it on the backstroke, for finish cuts. Both to save the tool edge, and to avoid a marred surface from the clapper bouncing along as the table reverses.
smt