Prasat Ku Kaew is the larger of the 2 with more information, and more still existing on the site. Prasat Phra Yun is right behind the city pillar in Phra Yun. There is a fair amount of detail on the little bit left.
Once again The Tourism Authority of Thailand continues to ignore many interesting sites in Isaan. You would think that sites listed in the Royal Gazette" might be worthy of a listing,
Also the city pillar in Phra Yun is more interesting than the one in Mahasarakham.
Go to the album in Picasa web to view the locations