It's a question of Performer/AFB vs Thunder/AVS, Performer is hit or miss, & I've been involved with a few for customers that were either never right or a major PITA to get
right.....one guy tried one too many stabs at it & took a hammer too it,LOL!!! The Thunder seems to be more hit than miss by far, and no flopping counterweights vs the
adjustable spring tension....................that being said, the 462 camel-back Chebby heads I did got a Eddy street TR w/a pair of 500 dual Performers, and worked great
(even tho the accel pumps started letting fuel shoot up thru the covers and onto the windshield!....where's that water comin' from...is it raining?... what the?....)