Sorry i misread your first post, i thought you had a spreadbore holley.
And you dont want a double pumper with most automatics. How high of a stall converter do you have? I've tried messing with a 650 holley vac sec, a used one. I've never had any luck with previously abused holleys for some reason which is why i still run my 650 avs edelbrock. Prepare to cuss a lot with venturing into the world of holley lol.