um, you can get a mass air harness, and computer(A9L) for less than 200 on ebay...
In my opinion, the tranny rear and body are worth more than that.
Mass air is only necessary really if you plan on adding a cam and power adders.
Speed Density is fine with bolt ons, i have full exhaust and upper intake on my speed density fox.
If you plan on adding a cam and a supercharger or turbo, then go for it, if not.. not worth it.
EDIT: To add to my post.
300 rwhp is not easy with just bolt ons. ive seen foxs go high 11's and low 12's with bolt ons.
If you do supercharger, then go mass air.
You can get the computer (A9L), harness, maf, and tube for the intake on ebay , like i said.
As for tuning, you can tune the A9L comp, but, aftemarket computers, are like 300 at most... which would allow better tuning, if i ever go mass air, im not gonna go A9L, im going aftermarket, in the end, its cheaper..
When your doing things like changing mass air flow sensors, there tends to be, alot of having to tune the maf for the injectors.. stockers are 19lb i think.
I would personally sell the car as a roller, and go with a aftermarket comp.
2007 Ford F-150 STX
DIP Phantom 22's / 305/40/22 Falkens
FX2 Front Valence / DJM 2/4 Drop
Carriage Works Monster Billet U/L and Flowmaster Dumped
Spending money that i dont have, to buy things that i dont need, To impress people that i dont know.