A repost of one i wrote back in May of 2008; but the information is still the same.
An AC-Delco 43-2XLS will work if you can find one (NGK BPR7ES interchanges). Starting in 1996 AC-Delco renumbered all of their plugs using only numbers to form an undecipherable matrix to assure no one used any of their plugs except as a direct replacement as the heat range information was lost. With an AC-Delco plug the bigger the number the hotter the plug. The old code was contained in this information I cut and pasted from AC-Delco's web site:
The ACDelco Spark Plug Identification Table
Prefix and suffix letters are used to identify a specific type plus the numbers relate to thread size and heat range. For example, the R45TS spark plug shown is:
· R = Resistor
· 4 = 14 mm Thread
· 5 = Heat Range (range 1-5 start with a 3)
· T = Taper Seat (No T for your gasketed plug)
· XL = Extra Long Reach, 3/4" fully threaded
· S = Extended Tip
I agree with the spark plug gap as well though if you go to an HEI (pertronix isn't a true HEI) gap it for 0.040"