Wanted to get a list together for relatively inexpensive and easy mods to get more HP from the stock L48. Not looking for a cam or head change.
Please feel free to add your ideas.

1. Intake manifold: 4-10 hp ?
2. dual exhaust/mufflers: 10-15 HP ?
3. headers: 10-15 hp ?
4....

I wouldn't bother with the intake manifold, without a cam change you won't see any improvement worth the trouble. I would work on getting the cowl induction to be functional like the 73-74's. True dual exhaust is probably the best mod you can make, headers will also help. Plus a good tune-up, bring the spark advance in sooner with aftermarket springs (not weights). Joe

joe the 76 did not have cowl induction cam,and a good set of heads

I agree with some. Headers and dual exhaust will pick it up over the stock pieces. I've seen headers gain 20 tto 30 HP on some engine combinations.

You already have an action plus intake, which is a decent intake, but at this point forward it will only flow as much air as the heads will allow the pistons to breath in on the down stroke.

I would really consider a head and cam change. If your concerned about the original look of the cylinder heads or having them worked on then you need to consider this.

You can get GM cast iron heads that have been reworked with valve angles larger valves that will breath better then the stock ones currently on the engine. The money for them is still fair. You could also take them and do some port work after buying these. I've seen ported steel heads that flow as good as if not better then some aftermarket aluminum heads.

That combination, possibly with smaller combustion chambers to up the compression with a milder cam, in conjunction headers and dual exhaust and you will have a really good engine. I would expect 125 to 150 HP gain.

Face it, after 1970 our small blocks were not built for much performance, but were part of the emission compliances starting to be set forth by our government.

hmmm.... I'm really cash poor and down time is an issue. What kind of $$$ would a head swap cost. What about porting the stock heads ???

A set of Edelbrock heads and a cam will cost about $1100 if you do the work. How many miles are on the motor now? Dual exhaust is the first thing you should change, next would be cam and heads. Headers would make a nice addtion after that.