I have a 53.
Does the 53 Block apply to the HO motor as well?
Negative. I have a 2001 HO and the block # is a 56 out of St Louis. All HOs came out of St Louis. 53 blocks came out of Mexico if the rumor is correct. I am pushing up against 190,000 now and still have my orginal VP-44. Never lost a LP, but I did replace it at about 30,000 with a FASS.
I picked it on July 3rd of 2000 right after the 2001 models hit the street.
53 is the block casting number and some have a tendancy to crack. You are in the build date for it, so check under the VP44 just above the oil pan for a number 53 cast into the block. If you do find 53 it doesn't mean your block IS going to crack, just that there is a possibility. I have 193k and no crack yet.