70 Nova, you have a Good Block for Rebuild, Like the other post says, your 2-bolt main is Plenty good enough. I love 350 Engine's , they are strong and plenty fast.
Good Luck with your Rebuild, I am also rebuilding a 350, and it is a 4-bolt main block. I did not know it was a 4-bolt main block until my friend brought it to my house.
Good Luck Hot Rodder!