At 50 mph or less in top gear,with 3.23s your carb will be working on the low-speed circuit only. You could take the main jets out, and it wouldn't make a difference.
So what to do?
Well firstly you need to be sure that you are not trying to cruise with too much advance. So with the car in park and fully warmed up, rev it up to the rpm that you noticed the problem. Keep it there and check the timing. Then disconnect the Vcan, and recheck the timing at that same rpm.
Let's say you have 3.23s, 25.5" tires and had a problem at 45mph. The rpm would be, I'll guess 1800ish.At 1800 your 360 with low compression will not like too much more than 35/40*.And the way it complains is often mistaken for a lean misfire.It will like 30 to 35 degrees tho. With higher compression it might be OK with 40*, or even 50*.
So if you are between 30 and 40 with the Vcan included, you are probably ok.If you are less than 30*, then the Vcan may not be working. To prove it; with the engine idling, and the timing lite hooked up, just suck on the hose and watch the timing change.Or hook the hose to manifold vacuum and again watch for the timing change. No change means the can is junk.
So after you get that ballparked, you will need to check the fuel. And the way I ballpark that is to engage the fast idle cam to put the rpm back into the trouble zone. Then reset the mixture screws for smoothest/ highest rpm. Then richen them up 1/8 turn. Return the throttle to idle. If it runs like crap, your T-port sync is out.(See below.)
But first take it for a cruise,even if it idles like crap.
The PV should be totally dead under cruise situation. You could be running a plug in there. However, if it had a perforated diaphragm, it would be dribbling fuel out the main nozzles,any time the engine is running, and perhaps after shut-down too.
But here's the thing, if you have advanced the idle timing, then you have also advanced the power-timing, and all the timing in-between.The power-timing has to be limited, to prevent engine damage. So stay out of WOT until you get the bottom end figured out.
And IMHO, if you can idle your 360 at 18inches of vacuum at 700 with just 10* of timing, the Bit of a cam would have to be a wee,wee,bit of a cam.
I would start by proving that neither Vcan nor the PV, is perforated.And then I would set the T-port sync. And then roadtest!