With all those mods at once you will never know if the heads were responsible for the gains you will see, headers in particular will gain you a lot along with the catback. The b-body cam is small and a torque monster, but you can take a big step up before anyone notices it was changed. I have a ZZ3 cam in my car and in normal driving it is just like stock. Other gearheads that know it is there say it sounds stock, yet is has 17degrees more intake duration, a whole lot more cam without a single drawback so if going into the motor like you will for heads why keep the stock cam? The ZZ3 cam was even great with 1650 stall and 2.93s.
The guy who reported losing power with ported aluminums on a stock b-body cam has run 10s with a relatively mild setup in his Impala and is the only heads/cam Impala we know of in the 11s NA(same car differnt motor), he knows a hell of a lot more than me and you.

Oh and another guy tried LT4s with a stock cam and dynoed less with 93 octane tuning than my car did with 87 octane tuning(same tuner), both of us with stock exhaust manifolds, similar intake and exhaust systems.

 

I was mistaken the one guy dynoed less than me with AFR195 and an LT4 intake, I thought he had GM LT4 heads

His mods mine
LT4 Intake stock
52 MM TB stock
AFR Aluminum 195 Street Heads stock
Dynomax Cat Back same
Home Depot / K&N Intake similar pvc too drilled stock airbox and dropin K&N
1.6 Ratio Rockers 1.5 roller Proforms
PCM For Less Tuning 87 octane pcmforless
Throttle Body By Pass same
New Plugs, Opti, and Taylor Wires few thousand on plugs, 50K on opti, 15k on taylors


He dynoed 243 I dynoed 263, his was a little rich and mine was very good, he had a broad peak of 285tq, my car kept downshifting so the best I got was 285tq already dropping. The stock exhaust manifolds are obviously choking both motors.
The other guy with the ported aluminum heads as I said is quite accomplished racing his Impala and the heads were done by Joe Prince so they were good and he knows what he is doing.

 

i have a 5 speed so im not worried about needing a stall. if me and my wife get enough back on our taxes i will get a le1 setup. i heard his cams sound awsome because they have a smaller lsa than most. i need to get at least 15 -20 mpg. so i dont know how this setup will work for that. from what i've read about these combos it should make this car a monster. .
my wife is already afraid?spell to floor it.

 

I am running Agistino Ported iron heads on my 96 Impala SS. They flow 267cfm's intake and 206cfm's exhaust @.550 lift with 2.05/1.60 valves. They outflow my ported set of AFR 190's with 2.02/1.60 valves. You can cut iron heads more than aluminum. On my 357ci LT1 I gained over 50 hp going to these heads and a CC224/230 vs stock short block with the ported AFR's and a CC330/236. 426 RWHP with the new setup. Good luck.
HVY SS