66 dodge monaco fender tag breakdown and build sheet

I got this car from my father(original owner) 2years ago. It would be nice to have the the build sheet and I checked a various of locations, including under the rear seat and no luck. So I looked at the fender tag I got most of the info from the tag but unclear about couple of codes.

Here goes, Can someone please fill in the blanks. the fender tag pic is attached.

If it matters, this car was built in Canada. From what I can tell, I can not order a build sheet from Chrysler Canada as they never kept them on record. Chrysler USA did.

a6=Center console
b4=bucket seats
d6=??

A6 = 383 4bbl
B4= ??
C5=Torque Flite automatic transmission
E3=Cleaner air package
R1=Radio - AM Music master/ economy 2watt
T7=Tachometer
Y1=??? front licence plate?

SO NUMBER
429 = Schedule build date April 29, 1966
00372 = Shipping order #

BDY "DP27" = Polar-Monaco, Premium, Convertible

TRM "P4X" = Premium black Vinyl bucket seat interior.

PAINT "PP1B" PP1 = Bright RED, but what is the extra "B" for?
Attached Images
 
Author: Labradorian