Honda-SOHC

I have a 1975 K registered CB750  -   The engine is and came dismantled with the engine number on casing starting with 278.... which looking at J Wyatt's book indicates it is off a K7 - it is not an import -   Ideally i would like to put an earlier engine in which will be in keeping with frame .   Does anyone know if engine is same or parts from later engine  will fit earlier engine-  ie are parts interchangeable?

Also, I have an original genuine Honda 4 into 4 which is off i understand a later K8 model,   three of the pipes are superb - one has a slight graze -  i think someone must have come off the bike and probably never used it -  I bought as i thought they might fit my earlier model but there are differences -   Would anyone be interested in a swap?

Hello all

Bought a 1975 registered 750 K2 (UK model i think)      Engines was in bits but is not original to bike   - I think it is off a 1978 model    Does anyone know of an earlier engine for sale please -  looked on ebay and unsure about condition    thanks