If you mean the the LSI block (circuit board) then they sometimes are interchangable with the M154's . The CSI' s are also semi interchangable
M158's are on thier own as are M354's (different fitting lugs)
Normally the LSI will have either a white or orange dot on it. Orange being for M158 and white for M154/159. Sometimes they are without
I have just written my results here on PCS if it is of any help?
http://pocketcalculatorshow.com/eve/for ... 1920997941
I have found through all this that this particular build of Module is real tiring :)

