Found a Replacement Battery
After 5 years, my original Delco battery finally died. I read several posts stating that only Delco made a replacement that would work for us.
For everyone'* information, after hunting around I found a replacement battery for the 2000+ Bonneville at Sears. Their DieHard International Group 79 #3379 is an exact match, including the top vents that we require.
The 3379 has 800 CCA, and an 8 year warranty (with free replacement for the first 3 years). Cost is $99.99.