Using a router and a straightedge clamp to square the ends of the core slab went better than anticipated. With some fussing, the straight bit worked like a charm, giving me a crisp step down to run the bearing on the pattern bit against. There wasn’t even any chipping on either first pass with the straight bit.
Unfortunately, the pattern bit didn’t work as well and I did get some blowout on the second passes. Nothing terrible, but I was kicking myself for not first scribing the ends (to sever the fibers and prevent chipping). No harm, no foul, though, because I still had to plane the front face square to the underside. All in all, I’m very pleased with the final length of 71 7/8″, which will be further augmented by the inner and outer jaws of a quick release tail vise.
The core slab, now S3S with only the top to go, is approximately 4 1/16″ thick. Assuming the slab doesn’t move any further (it cupped very slightly in the week after initial thicknessing), I doubt it will take more than 1/16″ to flatten the top. At any rate, anything over 3 1/4″ validates my choice to use 2×10’s instead of straight 2×4’s.
I’ve already created the mortises on the back edge, and I’ll be creating the front mortises over the Eastern weekend.