So I went to the auto parts store the other day and requested AC Delco R45TS plugs to replace the ones already in the car. While swapping them out I have noticed that the new plugs are a little bit longer than the ones I pulled out. Would there be a difference in plugs if they were for aluminum heads rather than cast iron?

I attached pics of the plug comparison, along with a shot of the IROC just for kicks.

 

Lets start by decoding the plugs. The 45 is the heat range, these are pretty hot. The TS is for extended tip.
These are correct for iron heads. If you have aluminum Corvette heads, you should start with RC12YC plugs.
If you've done cam and headers and so on, iron heads should consider R44TS, aluminum I'm not sure.

 

Thanks for the reply, the only reason I bought these plugs is because I couldn't decide whether or not to buy E-3's. The only thing I have added as of today is an MSD 6A, and coil, other than a chip, cat back, and air foil, its pretty much stock.

 

I don't think you need colder plugs with that combo. I don't think you'll find any benefit from E3s either.