R45 is a hotter plug than the R43. R44 used to be a good choice, but I've heard those are no longer available. If you have HEI, Champion RJ18YC6 (18 and 19 are hot plugs in the Champion scheme) works pretty well...or it has for me and for what it is worth, Mr. Tom Langdon agrees on this. A colder plug is designed to transfer heat from the plug to the head faster (which keeps the tip cooler--hence doesn't burn off deposits as well). A hotter plug transfers heat more slowly back to the head so the tip and the ceramic region above it up to where the conductivity zone is located remains hotter (which in this case might be better). Good luck.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end