I found this on a group that has knowledgeable members - John
MOTORCRAFT
PART# / HEAT RANGE AWSF-32C / stock heat range - copper plug AWSF-22C / 1 Heat range colder - copper plug AWSFA-12C / 2 Hea range cooler - copper plug AGSF-32C/ Recommended for FRPP heads(not sure on heat range)
NGK
FOR 99+ CARS w/ .708 thread depth PART# / HEAT RANGE TR-55/ 3951/ Stock Heat Range TR-6/ 4177/ 1 Step Colder BP7EFS (PN - 3526) two steps R5724-8 (PN - 7317) two and a half steps R5724-9 (PN - 7891) three steps R5724-10 (PN - 7993) four steps
PART# / HEAT RANGE w/ .750 THREAD DEPTH R5671A-7/ 4091/ stock heat range BR7EF/3346 / 1 step colder R5671A-8/ 4554/ 1.5 steps Colder R5671A-9/ 5238/ 2 Steps Colder R5671A-10/ 5820/ 3 Steps Colder
AUTOLITE
PART# / HEAT RANGE
764s
/ Stock
103s / 1 heat range cooler AR94
/ 2 heat range cooler AR93 / 3 heat range cooler AR92 / 4 heat range cooler
CHAMPION
PART# / HEAT RANGE YS-59C / -3 or -4 below stock heat range
DENSO
PART# / HEAT RANGE IT16 / stock heat IT20 / -1 heat range IT22 / -2 heat range IT24 / -3 heat range