I just noticed that SAOimage doesn't understand the decimal format of RA/DEC so I wish there could be a choice of getting the sexadecimal or decimal (oldstyle / newstyle) format of the fitsheader somewhere in the fits configuration tab in KStars.
After some testing and googling I found that CRVAL1 , CRVAL2 , RADECSYS , CTYPE1 and CTYPE2 must be there.. maybe something more.
I hacked a bit with Python and set RADECSYS="FK5" , CTYPE1="RA---TAN" , CTYPE2="DEC---TAN" then SAOimage seemed to understand the sexadecimal coordinates but with a really strange aspect of space and that lead me to think that maybe CRVAL1 and CRVAL2 is also needed.