ThermoQuad vacuum advance port

Since you are wanting to add PVA, I am assuming that the carb is not being used on the original ELB engine. Throttle opening v load will probably be slightly different.
So I see no problem using the ECS port for PVA. Good to see you using the TQ.
If you are building a performance engine [ cam that has reduced idle vacuum ], I would urge you to at least consider MVA. There is a simple, 5 min test, that will show you the benefit. Simply warm up the engine, engine idling, rotate dist slowly advancing the timing. If RPM increases, MVA will be a benefit, no downside, & behaves the same as PVA at cruise.