Probably next to nothing just bolted up. Bigger TB and spacer on a stock engine with a bigger MAF might give you a couple horse power, but I doubt any more than that.
I broke in my 306 last year with stock injectors and MAF. Performer intake, 70mm TB, TFS #1 cam, ported E7's, and BBK LT's. After it was broke in, I took it to the track with the street slicks and was running 13.20's at 101-102. That weekend I installed #24er's, and a Pro-M 75. Went to the track and ran 13.0's @ 104, which eventually wittled down to 12.90's @ 105. So a MAF can be worth some if you already have some other mods.
i have gt40 heads and exhaust and i did the mass air conversion using a stock MAF meter. i got a 70mm MAF from a 98 explorer and wired it in and definately noticed a difference in my top end, it will pull clear to 6k if i let it.