Spreadbore Holley on a 350

[dwcsr]

I have a Holley spreadbore on my 72 350 and have jetted it back to 59's from 62's. The mileage was at 10 mpg with 62's now at 59's is get 13 mpg Has anyone jetted back further than 59 without burning a piston. I'd like to get rid of the black and maybe 2 mpg more. It did originaly have a Qjet on it but it was afu and I couldn't get more than 8 mpg. Neighbors thought I had put a diesel in it. Any help would be apreciated.