E-303 idles mean as hell I thought it was a mild cam.

[420nitro]

Lift is an important on P/V clearence. But not the only consideration. You can put in a smaller lift cam in then before and still hit the piston! L/C and duration also plays a large role if not more then just LIFT. Specially if you go from let say a 114 L/C to a cam with lets say...a 108-or even a 110.
As goes for the Manufacture saying max. lift does not indicate possiable P/V clearence problems. All that means is that the stock valve springs that come that head will have coil bind issues, not to mention other problems. You should always check P/V clearences when swaping cams too. But **** happens and I know.
As goes for custom grind cams...I always try to use them for varies reasons but sometimes off-the-shelf cams suit your needs just fine too.
MY .02