The 8" is a good axle for medium duty and works well. You could also swap in a 9" axle out of a 70-77 Bronco by moving the spring perches. The axle is only about an inch wider than the original 8". You could cover that if needed by using a/m wheels with more backspacing on the rear like I did.
As far as more power, these heads are very restrictive. Aftermarket better flowing heads with larger valves would be a big improvement if you are swapping cams and intakes. Or swap to hipo 289 heads or certain 351's. The big cam, carb and intake would not be very effective if they can't pull enough air through the heads. With the right parts, these little engines can handle huge cams, carbs and intakes and be real screamers when kept in the correct rpm range. If your car is mostly steet driven, stay away from the wild cams and carbs like stated above.
Do some research and make sure your combination works together. I built a 302 reading an old Jack Rousch recipe from an old Hot Rod magazine and all of the components matched very well. If your parts are mismatched you will be disappointed with the results.
__________________ '78 2+2, T tops, 302/C4, 9"/4.30, full frame | 
