On a stock 302, saying you'd get a tenth or more gain from just the meter change would be pushing it a little bit maybe, but in your case, I would bet you'd see atleast 2 tenths, if not even more.
Your engine is trying to breathe alot more now with the intake, heads, and exhaust opened up so well now, but it is unable to because of that tiny stock MAF.
Have you ever taken a look through a stock 5.0L MAF? I dont see how a lawnmower to have to breathe through that thing, not to mention an AFR headed mustang!
