Here is an article on somethign similar I found, "Speed Blocks". These use holley jets.
Magazine test (http://www.hotrod.com/techarticles/s...k_jet_changes/)
I found your exact question on a Chevelle board, but only 1 reply to it, which was positive "Had no trouble, worked well".
From a dealer site, looks liek they should be "referenceable".
The needle is completely adjustable and metering changes are easily accomplished once the embossed calibration markings on the needle are noted and referenced. Each of these markings designate 1/8th of a turn. By referring to a handy metering correlation chart included as part of the kit, one can accurately richen or lean the carburettor's main metering calibration. The carburettor can be tuned even when the engine is running.