With all due respect and trying not trying to argue. But I have used the BP6ES in my '72 Eldo and '70 Ambo since I got them in about '80. Was there a change somewhere with the piston in the 750 Ambo's?
Also per MG Cycle's listing for the BPR6ES:
"This plug is also the replacement for the discontinued BP6ES spark plug used on these models: V700, Ambassador, V750 Special, 850GT, Eldorado, 850T, T3, G5, SP1000, Caifornia II, Convert, T4, T5, Mille GT, SP II, CX100"
Tom