I feel you will have no disappointments or regrets going with 2 500cfm Edelbrocks. You will probably do some tweaking to them on your 408 but they will provide years even decades of trouble free service and are great performers. I have had 2 440 challengers with the CH-28 and 2 500s and the power and fun were thru the roof. I have a brother who is still running the 2 600s he bought back in 1992 (yes the carbs have been cleaned and refreshened a time or 2 since then.) His carbs first on an M1 tunnel ram 440 build in 1992 and then in 2006 when he built his 440 into a 512 but running the same tunnel ram and carbs. Im sure 2 Holley carbs will provide the same long term reliable service as well but I have experience with the Edelbrocks and am typing it here. I think we all know for absolute max power and the best ET the Holley carb wins.