Not found alot of information
But from what Ive found your motorcycle would appear to be either 1978 XS400E or a 1979 XS400F
As far as the 1980 crankcases are concerned, part numbers for 1978, 1979 & 1980 XS400 crankcase are all the same (1L9-15100-01-00)
Hope this helps a bit
Kev :thumbsup: