: It remains to be seen if it will stay straight.
Ronnie,
I think your on the right path here. Problem is the damn trees don't know they're dead yet! Construction ply is made up of plys peeled off the log like unrolling toilet paper. So when they come into contact with moisture they want to get back to tree shape and the plywood will cup or twist. If the moisture only gets to one side the effect is worse. If you heat the wet side it will drive out the moisture and the sheet will return to it's original form.

If you use water based glue this is probably what happened. Your heat treatment may have cured the problem. I'd let the thing sit a couple of days on saw horses where you intend to build. If it behaves, seal it with a couple coats of epoxy to minimize any futher moisture take up.

: I am still going to route the holes oversize.
This is a good idea. If you get any movement during your build you can realign the forms. To help to align the forms and stabilize them while being fastened, get yourself some cedar shingles. You can buy a bundle of #2's for about $10 and have enough to build a house or buy "shims" precut for about ten times the price. Rip the shingles to 1 1/2" and 2 1/2" widths and use them as shims between the beam and the sides of the holes in the forms. This is the same technique used by finish carpenters to center, plumb, square and level windows and doors in house framing. The general rule is that a door (or window) "rough out" should be an inch larger that the frame of the door. Hopefully, the framers are able to keep things reasonably square so an inch is enough! Shims from shingles are 16" long and taper from a featheredge to 1/2". You can fill a space up to an inch wide with these shims. Two shims are used to fill the space with their tapers in opposite directions so the they present parallel faces to the sides of the space. So you might use 8 shims for each form. This method allows you to make precise adjustments and holds things stable while you place your fasteners. With the crappy lumber available for building these days you'll find lots of uses for your left over shims.
Good Luck!
Geo. C.