Its not a matter of how little you can but how much, i would prolly say to be safe 70 or 80. If you bore to much out , the engine will run to hot, thus you need to be very careful and know what you are doing.
The Bore of a 350 cid engine is 4.00, the stroke is 3.48 inch..
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.
4.040". The standard bore is 4.00".
4"
Primarily the bore size. The 305 has a bore of 3.74 and the 350 is a 4.0 bore. They share the same stroke on the crank. And no, you can't bore a 305 to a 4.0 bore.
Bore it .030 over. A 350 has a 4 inch bore. When you go .030 over, the cid., becomes 355.
4.030"
350 block, 400 crank. Main journals must be turned to accept 350 bearings. Stock bore is 377. .030 over is 383.
3.48 inches.
4.060"
4.040"
355