Yes, it will help. But with 15" rims there is a max backspacing before the inside rim lip hits the upper control arm.
You have small bolt front disks, correct? What spindle are you running with what brake kit?
Factory small bolt disks have a narrower front track. And may put the rim just slightly closer to the upper ball joint than a 73-76 A-body large bolt setup. I've never compared the two.
With 73-76 A-body disk spindles with 15" rims, the max front backspace is 4.5" with factory. And it's close. You should run stick on wheel weights on the inside side of rim.
Also your front end alignment and past body work will factor on how much room you have with un-modified 67-69 Barracuda fenders. More positive caster typically brings the front tire toward the back of the car. Giving more front wheel lip clearance.
I think 225/60/15, 15x7 with 4.25 backspace will be really iffy for you. You should really mock this up on both sides before running it. If you can run a 15x7 with 4.5" backspace, that will help. Still no guarantee's. I'm not sure you can fit 4.5" backspace on a 15x7 hoop. Due to the width of the center drop out. Check with Collins Custom Wheels on Alondra Blvd.
I think 215/60/15, 15x7 with 4.25 backspace is a safer bet.
