Poor idle and off-idle performance after distributor swap

Ok, so car is running really good now. Better than ever actually with the new distributor. Here's what I did:

Tq checked intake manifold bolts. Got some movement on a couple of them but I doubt it was enough to cause vac leak.

Took out distributor, removed the curved-arm vac advance can that was using the hole I drilled. Put the standard VC-93 straight arm vac can, that utilized the factory hole on the breaker plate. My theory was that somehow, my cobbled-together distributor was the source of the issue.

Put everything back together, warmed the car up, advanced initial timing until it was happy and turned the air screws way out and with the car idling in D and the brake set (and warmed up) progressively leaned air screws until rpm started to drop, stopped there. Very oddly, I made a mark on the distributor for reference before taking it out to swap cans, afterward I put it in the exact same spot and it was like 10 degrees off. Weird that just swapping vac cans would drastically change the orientation of the distributor. My only thought is that the arm of the vacuum can was somehow interfering with static timing at idle. Not sure how it would do that.

And that was it. Car runs fantastic now. Timing mark still jumps around a bit, vacuum gauge is bouncy at idle too, but I drove the car several times around town and on the freeway and it ran very well through the entire rev range, climbing steep hills at low throttle, sitting at stoplights for a while, cruising on the freeway at 70-80, all conditions.

The new advance can arm is marked 6.5 (13 crank), and I am assuming that my 8.2-8.5 CR 360 probably wants more vacuum advance than that for best performance, but for now I am pretty darn happy with the Frankenstein distributor. My initial is 16 degrees right now, 20 mechanical. I think the engine may be happy with a lot more initial timing, but I am going to wait for a very hot day before I advance it any more. Today was pretty mild.