A thank you to everyone who provided input to my previous post.
Using a combination of techniques/advice offered, I did the following:
First, a screwed both boards to a sacrificial piece of plywood (Thanks Frank) with the boards spaced 17/32" apart (width of a 1/2" straight cutter and then some).
I then attached the fence to my router and ran that against the outside of one of the two planks (which is straight enough for these purposes) and made progressively deeper cuts until reaching the depth limit of my 3" (usable) straight cutting bit. After that, I moved the fence out slightly so the bit was no longer cutting the first board but the second, in a mirror image of the first (minor imperfections and all). After releasing the boards from the plywood, they went together like silk, no light shining through the (nonexistent) gap.
Thanks again to everyone who provided suggestions.
Joe
I'll post a couple of pics in abpw if anyone is interested, just ask.
jc