JAKE LEG: I made an extension top for my Craftsman (1950 s) saw I Got from my dad. I used a solid core door slab and covered it with laminate. I used it (extension table and out feed table) because it was heavy, dead flat, wood tool machinable and in the long run less expensive than using lumber and/or ply. I used an ivory colored laminate so that I could layout (pencil) sketches, dimensions of work stock, notes to self etc. and then wipe clean when done. I also found that by using self adhesive sandpaper that it made a pretty good "scary sharp" surface. Another benefit to the solid core slab is that I have drilled holes for bench dogs and holdfasts. The caution with that for me is to remember that the core is very dense particleboard and be just a tad more careful with the dogs and holdfast.
I did machine the two table slabs to accommodate an afermarket (Grizzly) rip fence and front and back rails. For peace of mind, where I needed lags or screws in stress spots I glued in hardwood plugs so that the threads would have a better purchase. The one thing I should have done in fabrication would have been to edge the slabs where they were not blind to the machine with thicker oak edging.
HTH