after repeated checks for gaps and refitting the two sides of the top together, it finally made a strong enough fit that the boards closed up pretty well.
So now to MacBeath Hardwoods for a few more large clamps, and then a complex ordeal sorting out the glue-up dance, which amounted to playing the game of jenga underneath each beam for a couple hours, but finally it's pressed tightly and drying here:
With that done, time to concentrate on cleaning up the two legs I cut earlier from the smaller length of beam. Takes some doing but still had some of the patina from the beam's original use left over. A few framing hammer dents here, some nail holes that have stained the wood from the rust there: