Thanks, guys, for the bump!
I got a few more parts from the seller:
That's a 26.0 post (it was used with a shim) with a really nice Brooks seat clamp.
Note the cable end cap with a little set screw! I've never seen one of those before.
Juvela, on the crank, my plan --I haven't done it yet-- is to get stainless steel hex head bolts, M5 thread. I'll file the heads suitably thin and polish them to a mirror finish, and screw them into the allen wrench holes in the existing chain ring bolts. I may have to tap them first. Am I making sense? It's purely cosmetic, of course. When I try it, I'll know whether it looks good or not.
On the rims, there is no way I'm going to source period correct rims. Too fragile, and too precious. The wheels I'll put on this first are Campagnolo large flange hubs with Ambrosio Elite rims; if the rim decals bother me too much I may remove them and slap bogus Weinmann decals on there.
Unworthy, quite right, the frame does indeed take a 26.6 mm seat post. I think I have a Campy Record post in that size. But I might just use the cool chromed one, shim and all.
I'm planning a bike tour for the week after next, and all my bike fiddling is taken up with getting my bike perfect for that ride.... so the Allegro sits ignored for now.