As I posted earlier, my Dodge Motor Home Chassis parts book lists BL-9Y as the correct plug for 69-75 440-3 engines.
I did find this elsewhere on the 'net:
I have a 1977 Dodge Journey motorhome with a 440-3 engine. My owner's manual lists the RBL9Y as the proper plug for this engine. Unfortunately, many auto places no longer carry this plug. Many do not even have a listing in their books. The champion RV12YC is an equivalent plug that can be used. I've used it in my motorhome for the last 15 years. I'm very happy with the performance and upon replacement I notice the colour of the plug is within the proper specifications.
second post:
I found a booklet with these specifications for the 1977 440-3 motor...
Spark Plug Gap and Number: .035" (0.9mm)
Champion: BL9Y
Resistor Type: RBL9Y
So it looks like RV12YC is the modern equivalent to the BL-9Y.
