I don't have any hard data, but while breaking in a motor a couple years ago I tried the following intakes (just to make sure they all ran ok & didn't leak for future use), same engine, 440cid, early vanilla heads, late 2bbl 192-199 duration cam, flat log exhaust:
* 428pi intake
* 390hipo intake
* Edel RPM intake
* Ford iron "Z" intake (nearly same as "T" intake)
I didn't record data but didn't notice any change in idle or vacuum.
I've also run the streetmaster, it was down 1-2" vacuum, no surprise being a single plane.