Personally I haven't seen or heard of spacers like that. The Holley versions have a special arm, pump cams and (of course) diaphram. The 50 would basically extend the squirt duration for a given squirter size. But 30cc pumps will cover most needs so I'd suggest starting with that. I believe the pink and green cams are the biggest for the 30cc.

For a 4bbl or dual tunnel ram application?