"...Any ideas would be greatly appreciated..."
The 455 engine you describe should easily make 400hp and 500ft lbs of torque. It should be a real tire smoker.
If this is not the case, then I suspect it is either not getting enuff fuel/air mixture, or is not getting enuff fire at the correct time. And, I suppose that the cam may have been installed retarded.
What carb ? Have you checked to be sure the butterflies are opening COMPLETELY, when the accelerator pedal is mashed to the floor ? Sure the secondaries are working correctly(if vac operated) ?
Initial timing(at idle) ? Total timing and at what rpm is it reached ?
Most agree that the initial should be around 12-14 degrees, minimum. And usually the optimum total advance is somewhere about 34-36 degrees, reached at no later than 3500 rpm. Many think it should all be in by 3000rpm, and some, of course, like it even sooner. The correct timing curve can make lots of difference in power !
If the deck height is up near zero, you have about 9.73:1 static compression. So, you definitely need at least 93 octane gas, or maybe a little race gas mixed in.
Compression Ratio Calculator - Wallace Racing
Here is the Lunati cam, which is the closest I can find to the specs you gave. It looks like a decent choice for a 455. But, I'd run Rhoads lifters with it, to give it a smoother idle and more vacuum and more low end off idle torque and power. I like for my bracket engines to have a decent, fairly smooth idle, at 800rpm, in gear.
So, does your engine feel weak at low rpm, or up near 5000rpm or both high and low ?
"...My question is will Edelbrock alum heads bring my motor to life?..."
You should not need alum heads. But, if the iron heads are not highly and efficiently ported, then alum heads will flow more fuel air mixture, therefore have the potential to make more power than unported 6x heads. One advantage of the alum heads is that you can run 10.5 CR without fear of detonation. Some run 11:1 without problems.
If you decide on alum heads, I'd recommend KRE 85cc D-ports.
Kauffman Racing Equipment
But, if you want a working heat crossover system, for cold weather driving, then the 87cc Edel D-ports are the way to go. The out of the box E-heads are said to have inferior parts. So, if you decide on them, most recommend that you buy some that have been built from bare heads, by somebody like Butler or SD Performance, with quality parts, and machine work. With bolts and shipping, these will cost near $3000, or even more, depending on level of porting.
Butler Performance - Edelbrock Aluminum D Port Pontiac Cylinder Heads
BUT, again, I say that the combo you described, properly tuned, with a GOOD Q-jet, SHOULD make somewhere near 400hp @ 5000rpm & 500ft lbs of torque @ between 3000 & 3500 rpm. If it doesn't, you need to find out why. Just swapping to alum heads alone, will not fix the problem. IMO
Here's an engine similar to yours, by a well known Pontiac engine builder.
455 Long Block