Std 340 bore is 4.040". This block is reading .023 - .024" over with the cheapo micrometers. What ever that is worth. To be sure, it should be measured with a good reliable micrometer.
Also, I think that your casting date is really 1-7-70. It is definately a 1970 model year engine. If it were a 7-7-70 casting, it would be a 1971 model year engine as the changeover is between June and July. Any casting/build of a block after July should be for the following model year.
