Would it help?
If your looking for more power a 4 barrel can help so do headers and other things.Or if you got the cash rebuild it stroke it better heads etc etc,It comes down to budget and power you want to have.Is your mustang a coupe or sportroof?
I'm not sure if you were already aware, but you'll have to replace the intake manifold to accept the 4 barrel carb. There are a lot of other upgrades you can do. How much power do you want and how much money do you have to spend? 
To answer your other question, I had a noticable increase in power when I installed my 4 barrel carb and intake. Maybe the single biggest improvement I made (I haven't regeared my axle yet).

To answer your other question, I had a noticable increase in power when I installed my 4 barrel carb and intake. Maybe the single biggest improvement I made (I haven't regeared my axle yet).
Just the 4-bbl carb isn't going to add a huge amount of power, at most maybe another 15 - 20 hp with the factory 4-barrel intake manifold, heads, exhaust, and cam. A little more with a good aftermarket intake.
Norm
Norm


