Eric sounds about right for 428 wall cores. 13/64" is just a snug fit with no real effort. If you want to sell it as having 428 walls you might want to have it sonic mapped. This will tell you exactly how far the block can go and also any coreshift the walls may have that will limit overbore. From the measurement you gave it sounds like a .060 411.2, 390 bore. But my math stinks and you better double check. A tic under std 4.13 428 anyway. For the most part 428 blocks I've had went .040-.060 over 4.13 std. A sonic map runs around $60 here. Even though the C or A is not on the back hopefully it will check out and have good thickness. For sure worth looking into if selling.

G.