Try www.keithcraft.com or www.gessford.com as they do lots of FE motors. I saw that Keith had mentioned recently that he has some S/O's around, and he also has the genesis blocks too.

As for the marine blocks, they are not true S/O's unfortunately. They are 427's, but they are not drilled as sideoilers (they have the hump along the drive side though, although not drilled). 427 center oilers are fine for street use, so unless you're really wanting to push the high rpm's, it's not necessary. On the flip side, I have an S/O in my Cobra, and I dig it.