How much is too much dual quad

Depends on cam duration and
Engine compression and total advance.

If you have big duration cam= no vacuum.
Might be better off with 2 480 cfm holley
Manual secondarys.

I have similar set up on 67 cuda 383 11:1
Open chamber steel heads ported.
550 lift 300 duration. 1.6 rockers solid cam
Have no vacuum. 50 Degree straight advance .2 480cfm Holley 50 cc pumps.tunnel ram
Can't get it running any better.....

Also without 3.91 gear or better you will lose little low end power for sure