Is your bike a UK model frame and engine or is it an import? A K registration wouldn't be a 1975.
Oops just noticed you said not an import. But it can't be a K7 if registered in 1975, we were still on K2 heading towards launch of K6 at that time. 🤔🤔🤔
If its a UK model, the engine numbers don't tally, as we never had K3, 4 or 5 in UK but the engine serial numbers kept running concurrent.