They're not steel, they're cast iron. The two terms are not interchangeable.

Nearly every new car on the market, maybe all of them, use aluminum heads. So to say they have no business on a street car is an opinion whose time has passed.

Specifically, your old X heads will flow something like 220cfm, max. They have a lousy combustion chamber. Rebuilding them to stock specs will cost more than $600, if I remember the last numbers bandied about here. Fully port them and you might reach 270cfm, max. One plus is you already have them.

A brand new Edelbrock head flows 247 max out of the box. Run a good CNC program or have an experienced porter do them and you're tickling 300cfm, max.

So with the Edelbrock aluminum head you are looking at a possible 60hp gain.
Other advantages to the aluminum head: all the aftermarket aluminum heads have improved combustion chamber shapes which make the engine less octane-sensitive.
Plus, you can add about a full point of compression with the aluminum heads, going to 10.5:1 or a little higher. This is additional power and efficiency.
Plus with the more modern chamber design you can run less ignition lead (timing) and reduce the amount of negative work done on the piston.
Plus, the aluminum heads weigh about 1/3 as much as the iron heads do, and the weight is saved from high on the front end of the car, where it does a lot of good. IIRC LA heads actually weigh more than B/RB heads.

There are the Edelbrocks, the Speedmaster/Procomps, Hughes' varieties, and the Sidewinder from Todd Marsh (Sasquatch on this board.) There are also the ProMaxx heads which are the same as the Sidewinders but are priced higher.
There are also the Enginequest iron replacement heads which work very well and have a Magnum combustion chamber that is pretty successful. I believe there may be another iron head out there, too. Problem with the EQs is they are pretty expensive.

Good Luck!

R.