If anyone is interested, I have FINALLY finished milling the cedar that
I had stripped out of our old solarium and off the side of the house
for our remodel. I posted the titular question back in October of
last year - it is amazing how little you can get done between the
months of October and February.

Ended up having to mill it into lap rather than t&g because of the
final thickness - 5/8" - which didn't seem like enough to support a
t&g. In order to maximize my yield from the wood I didn't cut to match
my joist spacing but rather will biscuit the ends of the boards and let
the joints hang in space. I figure the 18 years that the boards hung
either in the solarium or on the side of the house induced any twisting
or cupping forces to express themselves and the planing took it out. I
hope.

It was about 30 hours of trimming, ripping, beveling and rabbeting. I
think it was worth it. We'll see in a coupla years. Oh, yeah, wish I
had gotten that dust collector - the trips upstairs with the shop-vac
every 45 minutes to dump the dust sucked.

App