First SR1: appears to be from 1965, according to one of the manufacture dating schemes in use at the time, ... variations and exceptions do exist to confuse things though.
engine type was in production from 1967 thru 1976 so either we have some serial number confusion or other error in the dating scheme for this one.
Second LR1: is a closest neighbor of the SR1 in terms of manufacture dates. Yours appears to be the 3,738th LR1 unit built in 1972 if the conventions hold true.
engine type was in production from 1967 thru 1976
All parts are available for both of these units - they were (and remain) widely popular for alot of small utility power needs.
dieselgman