Did you try launching just above idle - like 1200rpm? sometimes loading the convertor up is not the best launch for 60' time etc.
Take you 600cfm with you next time and swap out to compare- you may be suprised.
I was just going to say that...lol. Nice job. I'm sure it has more tuning ET drop in it. Edelbrocks rarely are "just right" out of the box. You can quickent he secondary opening on the AFB design by removing some of the counterweight on the secondary air door. If you have gear and convertor, you may find it runs faster wiht it opening faster. It's a heavy package too, so you may also try adding a little initial timing and bolting the 600 back on. If you can gain .1 in the 60', you should lose about .3 on the full 1/4 mile. The 60' is key. And I think launching from just off idle will be better for you.