It would appear that they are the same.
I thought I'd give it a little google and I've found a site listing the SV400 parts fiche. My Russian isn't the best but part numbers should be the same across boarders.
The head gasket is, if its the one I think you're after and using the rear as an example; 11242-19F00 according to this site. Compare that to the SV650 and they are identical, this I deduce that they are one and the same part across engine size.
For reference
the SV400 fiche and another
SV400 model I do not know the difference. I crossed referenced the part number using
Ron Ayers and the reverse part look up. Please double check my workings for your own satisfaction.