Disc brake master cyl bore size.

It's too soon to worry about it.

If you pay attention,later, you will notice that almost the only time the booster does not assist, is at cold start up if the idle does not pull enough vacuum, off choke.Another time it might not work is when sitting at a long light, idling in gear, for a long time. But this is more likely to be a faulty control valve inside the booster. Almost all the rest of the time,there will be sufficient vacuum to operate the booster, provided that the check valve is doing it's job.
If you use one of the smaller bore M/Cs, the transition from fully boosted to losing boost is not dramatic. By the time it becomes noticeable You will be nearly stopped anyway.Stop worrying.
Besides; a .504 lift street cam is likely around 220 to 225 @050 so that size cam makes plenty of vacuum, once the Tport has been set.More than enough.Now if you had a short stroke Teener, um