Ok i know some information about Ghourgushti tribes, there is the sarkhel clan who are a division of Yousafzai tribe, Najabat Khan the famous pathan warrior was from this clan and this village he is the person who killed guru gobin singh during the shikh wars. Also there are the dilawarkhel and mattakhel clans who are from the utmanzai tribe they are also found in Jilalia and waziristan and are known for being bad tempered and warlike. Also there is the Anyatkhel clan who exist in a number of village in chach and are aslo found in Swat and Manwali, in chach this clan are wealthy land owners.
Nawab Najabat Khan did not kill Guru Gobin Singh - Nawab Najabat Khan died in battle in 1761, just before the Third Battle of Panipat, in which his son Duleer Khan took participation in. There was another Najabat Khan, who was a General in the Mughal Emperor Aurangzeb's army, who had indeed fought in the Battle of Bhangani against Guru Gobind Singh.
However, you are right that Nawab Najabat Khan was from Sarkhel clan and was born in Mohalla Ishaq Zai - the ancestral home still exists next to the Tandh. His older brother's name was Zabita Khan who remained in Ghourghusti whilst younger brother left for Hindustan for work. Later on, Najabat Khan called up other clan members to Kunjpura where he built his fort. Hence, the reason why Sarkhel's are now one of the smallest clans in Ghourghushti - most of them died in battle in India. I have a lot of information and facts about Najabat Khan through detailed research, and may one day write a book so that all Pukhtoons in Ghourghushti can be proud of.