There is 2 listed for 1979 but i dont know what the difference is.
Part # = 13150-40400
Part Description = VALVE ASSEMBLY,REED
Model Count = 12
PE250T 1980
PE250X 1981 
PE250Z 1982
PE400T 1980 
PE400X 1981
PE400Z 1982 
RM250-N 1979 
RM250-T 1980 
RM400N 1979 
RM400T 1980 
RS250T 1980 
RS250X 1981  
Part # = 13150-40300
Part Description = VALVE ASSEMBLY,REED
Model Count = 2
RM250-N 1979 
RM250-T 1980