I was basically referring to the common 6-7 speeds that are quite popular on our vintage bikes. It is with these that we encounter the Sedis and other chains from the later 70s to the 80s with no links. I am working on an 84 Torpado with low miles that has a very dirty and neglected and gunked up driveline. Taking it all apart for cleaning makes sense, and I like how the quick links allow it to go back together. So I am talking 6 speed chain and using a 6-7 speed link. With it being friction, I would think the link would be within .2-.3mm of the chain thickness. I was perhaps a bit more concerned about the pin diameter matching the pin diameter of the older chains.
edit;
I just measured the old chain to be 8mm at the pins and 7mm at the plates. The SRAM and KMC links I believe are in the 7.1- 7.4 mm range perhaps which I would think is close enough as it is slightly narrower which seems as though it would be safer that way. Pin pressed almost out to separate old chain was about 3.62mm as was the quick link. I guess I wanted reassurance that this was an acceptable practice.