I've sonic tested 4 stock bore(4.180) 413 truck and industrial block, none of them would go safely above 4.250 bore size in my opinion
I like to have at least .160 wall thickness on both thrust surfaces after boring
Never sonic checked that 413 block myself but I saw an operation ONE BESTER than that !
When I was west side down State Michigan there was a guy I knew who had a BUSTED UP block ......
Who pulled up sections of that block.... I saw areas in the cylinder walls - ON THAT BLOCK - that were near .250 !
