Due to the low CFM rating of the old 3 bolt style carbs (155-185 CFM for the Holleys) they were/are normally run synchronized rather than progressive.

In this type of configuration the idle and power valve circuits are left intact. This setup usually requires a pretty fair amount of fine tuning (with a vacume synchronizer guage) to get adjusted correctly.

There is a pretty good explaination of the process in Tex Smiths Hemi book. It deals with a 4 carb setup on an early Hemi but pretty much covers it all.