you would have to look at the internal design but usually there are 'things for the oil to catch on and let the air pass.
It could be anything like a perforated steel plate to something like steel wool. It will catch the oil and and let the air go on by.
I see a trend here,
years of blow by, building up an impressive layer of carbon on the pistons leading to pre-ignition. Higher pressures in cylinder = more blow-by = more carbon buildup = higher pressures...
Just buy individual pares of jets. The only kit you will buy is are two big divided trays with two of every jet. And they are not cheep a local autoparts store that sells Holley parts should have them in stock.
After you get the driving around jetting done you will need to rejet the secondary for wide open throttle. I would start out with what ever you have for a primary put in the secondary and see how WOT feels.
I confirmed with Summit that the carb shipped with 51 Primaries.
But they stated that Holley doesn't list any number for Secondaries.
This is getting ridiculous. Everywhere I turn is another hurdle.
I would guess / expect the secondary side are 51 also. I would not worry about them. Holley's can have anywhere from the same jets on primary and secondary to the secondary's being up to 10 more then primary depending on application and how it responds to full throttle.
You should also have a vacuum gauge on a long hose to see what your 45mph on a flat road vacuum reading is to make sure your power valve is correct.
Put the 48's in the primary and warm it up. Re tweek your idle mixture (and idle rpm if effected) then drive it. Pay attention to how it behaves holding a steady throttle. You want to go down in jets Untill you feel a slight surge on a flat road holding a steady throttle on the 35 to 45 mph zone, or you feel a hesitation when on that same road and you just give it a little more throttle. (Say like push down another 1/16 inch)
Once you find that jet go up one. If your fortunate to do this on a low 80 degrees day you will be in the normal temp swing.
There is a catch to all this.............once you know what "Correct" feels like every 20 degree change in temp you will feel the need to change jets. Like a fall winter and spring jet set, and then one for summer.
The blue gaskets are reusable. But with care the black ones can survive once or twice. You don't need to remove the metering block to remove the jets. Just remove the bowl and hold the metering block still and remove the jets it takes 3 to 5 min to do this. Its not hard at all.
I would buy two of each size from 49 to 46. They are cheep.