400 sb siamese

question, i got me a 400 sb siamese.
can i run 350 heads; and what cc?
also was told to block off steam holes between cylanders....
pro's n con's??

I have a 1970 Chevy 400 that I bored out .030, and used 327 camelback heads on. These are small chambered heads, but I've heard of people using 76cc chambered heads on the 400. I did not block off any steam holes in my engine, but since cooling is a concern, especially in high performance applications, I would reccomend the use of at least a 3 or 4 core radiator, ( I am using a 4 core with excellent results.)