Loafing,back when I used the 2 750s on my 350(not doubting what edelbrock says)I had a 67 camaro,there was another fella that had a gremlin with a tunnel ram and 2 500s.Our cars were similar in that we both had 350s,we both had small solid lifter cams, we both had similar gearing etc.His car ran low 13s my car ran low 12s.My car was raced regularly over a few years and I tried many combinations using 350s.I may quote a few times I turned with a little inconsistency,but that will be because it was at different times with the same car and different options.
The car ran 12.30s at 110 mph and it weighed 3380 with dual 750 carter(pre edelbrock owership)so that made the car 3550 with me in it.I used GM angle plug heads that were ported.The car should have been a little quicker judging by the MPH.I think that still works out to about 360 rwhp.
your heads are probably quite a bit better than what I had.
you will have to do the math and guess that 3 or 4 of our components that are different will add or subtract 5 or 10 hp each and thats exactly what you have,lol. I hope that kinda helps?