I don't think they did back then but im pretty sure they do now under that same casting number, 3970010 is available today as a low, low buck crate motor, it even comes with thous total garbage 883 head castings. LOL !
Yeah that's an 8 ... i would say GM decided for the made in mexico block they would make the 3 an 8 .
Also with the original 3970010 blocks the numbers were bigger too so they didnt just swap a 3 for an 8 when they added in the made in mexico
As far as i know the stuff that comes off the Mexican assemble lines is every bit as good if not better than plants in america
Wish i could help you with the CD8011061 number as that would tell you if it came from a 3/4 ton or not (maybe its just a crate motor number) and is a 4 bolt, theres an admin here who has brokin down numbers for a few people maybe he can help you