Again, thanks to all of you for responding to my question. It's nice to have a reality check, you know?

You all offered a good amount of food for thought. I went back to the drawing board, took a closer look at my issues, and reconsidered things. Here's the update:

The timing is actually really accurate... except at idle. At 3500 rpm and 30 BTDC the timing only flutters half a degree at the most. Furthermore, at 10 BTDC and 30 BTDC at full advance, and with the fuel/air mixture adjusted just so, the spark plugs indicate nice clean combustion. There's a slight amount of pinging if I head up a hill at 25 mph, throw her in 4th, and stomp on the peddle just so, but at worst it will just barely pings a few times and then the pinging goes away, and I actually kind of have to work at it to make it happen. However, when she's idling the timing does bounce around a bit... about a degree or two. It sounds like that's normal. Looks like I'm just being too picky.

I'm still having breathing issues, though. At speed she runs like a Swiss clock, and as long as I set the idle to about 1000 rpm she's really happy... although that does contribute to run-on when I shut her down. She's really touchy about temperature at idle. On these cool mornings (I live next to the Columbia River) she idles noticeably higher, but as the day (and the engine compartment) heats up, she idles progressively lower. And like I said, she doesn't like to idle below 1000 rpm either. Perhaps this is just part of the characteristic of the Isky VV71 cam? At low rpm she'll run fine if I give her a little throttle here and there, but if I just let her sit she'll peter out and die. When I pull the air cleaners I can see the pistons on the SU's slowly drop when that happens. To me this indicates uneven vacuum. As I already have a restricted nipple, and as the only issue is that the hole looks a bit wide to me, Chris recommended I just fill it with a dab of JB weld, then drill it to size. I look forward to trying this out this weekend. My plan is to start with a 1mm hole, see if it fixes things, and go from there.

Again, thank you all for the advice, and for sharing the story of your experiences. What a long strange trip it's been.

Ry
PDX
'63 544