I pulled the casting number off a V8 from a '75 Nova.  It's 346260.  I checked mortec.com, but couldn't find it listed.  Would this be a 305 or 350?  

you might want to look a little closer at the number. sometimes the 3,6,8,9 all look the same. i checked several websites, sb, bb, and their heads and came up with nothing. i'd look closer, or if you know what your doing pull the head and measure the bore. 350 has a 4" bore and the 305... well its smaller than 4".  

I don't see anything close in a six digit casting. Do you have the stamped number from the right front of the block? That may help.  

I've been having problems reading the numbers off the engine.  I'll try to see if I can pull some more numbers off and repost them here.