The six 1.5 inch brass core (freeze) plugs in my 460 were about .460" deep and I could not get a good outer diameter measurement as they were distorted from removal but were slightly over 1.50", they were Dorman part number P28C.
Replacements from Jegs were also brass, Pioneer part number PC30B, but were thinner, .35" deep and larger 1.525" diameter. The holes in the block are measuring 1.495-1.497". This plug seems to be for overbored holes. I did not want to take a chance on cracking the block trying to hammer these in place.
The brass plugs from NAPA were from Federal, part number 219-8133, PC133, and were even thinner, .30", and diameter was 1.507". This seems to be a better fit for the diameter but is not very deep.
I have heard that for marine jet boat applications the deeper plug is better.
What plug size, part number and source
are other 460 owners using?
NAPA recommended Permatex High Tack Gasket Sealant for use on core plugs.