Bore it .030 over. A 350 has a 4 inch bore. When you go .030 over, the cid., becomes 355.
4.030"
You can bore a 350 .090 over, but the thing is the bore is so big that the cylinder walls are about a hair line thickness apart. In order for the engine to accept the bore and punishment of the shear power, the 350 Block must be casted with extra carbon to strengthen the block.
4.060"
4.040"
355
it is a 30 over 350
408 and it really cant handle that
20/350 = 2/35
Its a 355 cubic inch
4.040". The standard bore is 4.00".
Most builders feel it shouldn't be bored over 4.065".