Is it just plain al like the rest of teh block?

 

?... I dont understand the question...

 

they are not aluminum, notice how they are so quick to rust when exposed. they are steel of some sorts.

 

The sleeves are definitely ferrous. Put a magnet to it.

They're probably made of ductile iron. The sleeves are cast into the block. On the outside of the sleeves, there are ribs that secure the sleeves in place to prevent up and down movement of the sleeves.

There also might be an improvisation to facilitate the expansion of the aluminum around the sleeves to keep the aluminum from shifting the sleeves when it expands faster than the iron sleeves.

I've got a picture that shows the ribs in a way overbored B-block if you care to see it.