aluminium head questions

I've searched and read as much as I can about the topic but I have some specific questions about my build that I couldn't find answers for.

My car:
'74 Scamp
3400 lbs
4.10 gear
727 w/ 3000 converter
7.67 sec 1/8th mile (haven't run 1/4 but expect low 12's)
440 .030 over, 3.75 stroke
452 heads (open chamber, 88cc)
9.5 compression
hydraulic flat tappet lifters
Comp XE274H cam (.488/.491 lift, 230/236 duration)
1.6 rockers (makes lift .521/.524)
Edlebrock 6 pack intake
holley 6 pack carbs
custom built headers (1 7/8" stepped up to 2")

The main things to be gained going from 452's to AL:
-can get closed chamber vs open for 452
-about 290 cfm intake flow vs 205 or so for 452
-up to 10.5 or so CR compared to current 9.5
-lighter

What I'd like to acheive:
Gain about 50 HP while keeping the look of the 6 pack setup and still drive good on the street while running 11.60's or .70's. My car is probably 90% street driven but even when street driving I'm the type that likes to know there's a lot under the hood.

Based on my build and 1/8th mile time I think I have about 450 HP. I'd like to reach 500. I'm considering aluminium heads. Is it possible to gain 50 by just swapping out the 452 heads for aluminium? Or, would I have to ditch the 6 pack intake and carbs in place of a single plane intake and 4 barrel?

My headers are custom built and very close to everything (valve cover, torsion bars, steering column, starter, trans, spark plugs, etc) so it's imperative that any head change doesn't move the exhaust. Along w/ that, it seems like a lot of aluminium heads have angled spark plugs. I'm not sure that angled plugs will work for me.

So, is there a head that will give me 50 HP w/ the 6 pack setup and not affect my exhaust (no angled plugs)? If angled plugs are my only option, can anyone tell me how much angle they have (a referrence to the amount that the end of the plug would move would be great).

How much compression can I safely run and still have a well-mannered street car?

All suggestions are welcome. Sorry the the long read.