Frazer Serial Number Book shows this
B1-6 s/n
1,001 - 31,200
B1-6R s/n 50,001 - 52,600
B1-7 s/n 60,001 -
80,000
B1-7R s/n 101,000 - 104,650
B1-7RA s/n 120,001 - 120,450
Serial Numbers above were built between March 1946 to February 1949
Earlier Models started in 1945