OMG, a .040 over bored 1969 block is not going to hurt anything. I bet you could seriously bore it .100 over and it would live forever. Remember in 1969 they used REAL Iron nowhere near today's materials!
Shoot I have offset bored a 1973 318 to 4.040 and made a 402 stroker out of it. There was PLENTY of material left in it! That is a .130 over bore !