All,
I spoke over the phone with a representative from Lares and they confirmed the initial answer was just a brain-fart. The boxes are cast aluminum.

Now I just need to find the best source. As Jeremiah notes, RockAuto is currently out of stock of the new box but does have stock for a reman unit. I intend to keep my original box though, so would need to eat the core charge.

From a ratio standpoint, 16:1 is too much for me. Although my motor has aluminum heads, intake, and it still takes some effort to turn the car around in my tight drive (side load garage). I have at times though about 20:1, but it is a big jump in cost and a bit of an unknown. 24:1 is familiar and the car is mostly a cruiser with occasional visit to the strip (ie no twisty stuff). Just getting the steering tighter than it has been will feel like a huge improvement!