Well first we know it's not a sideoiler. Yes, the ribs would indicate a "service block".
Some numbers around the
oil filer area will help nail down what it is. Look for something like C_AE _.
A few pics of the underside of the block might help as well.
Also, since it is stripped, take a flashlight and look into the freeze plug holes for a possible casting that says "428" on the outside of the cylinder casting.