March peformance pulleys

Got a full set ( 4 pulleys ) coming in the mail from March Performance . They 'estimate' between 14.5 - 20 rwhp freed up. If I went with just the two pulley kit , they say 12.5 - 15 rwhp freed up. Does this sound hoax like to anyone or do these sound like solid numbers ? I doubt they'd lie since they are a major performance company but I dunno. Anyone else done this to their third gen F body ? After I get mine , I'm shootin to the dyno upon completion of install and we'll see what they run. Shiny black powdercoated pulleys will be a nice change from all the chrome i've thrown under the hood.

Let me know what you guys think about this.

I was reading Hot Rod magazine in skool a bit ago on the Mustang Mach 1 project car or something, and they actually lost power from a pulley setup. Something like they gained 20ish hp with headers and an intake, but when they put a lightweight aftermarket pulley system on it they lost about as much as they gained with the headers and intake so it evened out to what they started with.

I hear that pulley kits and such add about 7hp to the ground, but with that test and dyno readings off the Mustang they did I guess it's all on the car and what engine your doing it to. Don't know if this helps much but I thought I would just throw that in.