All the Holley tuning books I have point at 390 to 450cfm for an engine of 350(ish) ci and a fairly low state of tune.
The 600cfm Holley I've got on now seems way too big.
American jeepers, however, simply won't have it.
670cfm Holley Truck Avenger on a bog stock 360 is typical.
I met a guy (over here) who ran a (std) Jeep 258 six with a 600cfm carb on it.
I like overkill but thats just plain silly
I've been searching the IFSJA forums on V8 carbs.
The more posts you read the more confused you get.
Consensus seems to be that the Edelbrock is a good on road carb, but crap off road even with the off road float kit.