from soch4 site info
CB750 K4 1974 Jun 1973 – May 1974 E2300001 frame: 2300001
CB750 K5 1975 May – Dec 1974 E2372115 frame: 2500001
looks like a 74 to me, hard to believe that frame got one of the first 100 or so motors
from the 75 batch as a replacement, but its good information
when reading the supplement in the manual
is there a vin plate, whats the production date? m/yy, upper right corner