iron head try to stay under .500 gross and there should be no issues , over that you need to check close , roller cams have higher lift than most flat tappet cams and require cutting the exhaust guides down and use seals on them
and its not about messing up the vac , its about how much rpm the cam needs for a good idle as a computer controlled car has a set idle rpm that cant be changed without a chip reburn as it could be on a carb , thats why it was recomended to call turbotweak as he can set the idle wherever you want (or moreso where his experience tells him it should be ) but i can tell you that cam is very mild and doesnt need any idle mods to the chip to idle good when using a tt chip