What is the best spark plug for a V12 E type with manual trans

I am helping a friend with a V12 E type convertible. The plugs are black and sooty. The car is hard to start, and the idle is very rough. The current plugs are NGK BPR6ES. Would a hotter plug help?
Does anyone run a BPR 5 EIX with good results?

Welcome Jack.

I guess it’s a carb engine?
IMOHO you must find why it’s running rich causing the sooty plugs.