so ... one in the piture is part 45115-392-003. £205 from CMSNL or theres a german one on eabay for £100. According to OEM it fits all of:
CB750A A (76) MOTORCYCLE, JPN, VIN# CB750A-7000001 TO CB750A-7007331
CB750A A (77) MOTORCYCLE, JPN, VIN# CB750A-7100001 TO CB750A-7110560
CB750A A (78) MOTORCYCLE, JPN, VIN# CB750A-7200001
CB750F A MOTORCYCLE, JPN, VIN# CB750F-1000002 TO CB750F-1015054
CB750F A (76) MOTORCYCLE, JPN, VIN# CB750F-2000003 TO CB750F-2022317
CB750K A (77) MOTORCYCLE, JPN, VIN# CB750-2700009 TO CB750-2729534
CB750K A (78) MOTORCYCLE, JPN, VIN# CB750-2800001
Top Bracket is 45104-405-000. No sign of any for sale anywhere
Fits : CB750A A (77) MOTORCYCLE, JPN, VIN# CB750A-7100001 TO CB750A-7110560
CB750A A (78) MOTORCYCLE, JPN, VIN# CB750A-7200001
CB750K A (77) MOTORCYCLE, JPN, VIN# CB750-2700009 TO CB750-2729534
CB750K A (78) MOTORCYCLE, JPN, VIN# CB750-2800001
Pin is 45116-367-690, £46 from CMSNL
So about £300 for new ! ... bloody hell. Think I'll frame mine