Yes, but I didn't want to comment; Muslims, especially Pakistani Muslims, think they know all about Indian/South Asian sociology and correcting them is not easy; I'd rather stick a knitting needle in my eye.
This clan exogamy is known as gotra among caste Hindus (it doesn't exist elsewhere). The Jats have been in the news most often about gotra, thanks to their damned khap system; khaps are gotra-based panchayats, with wide powers of corporal or even capital punishment (needless to say, with no legal sanction whatsoever). How it works is that I, from Kashyap Gotra, may not marry anyone else from Kashyap Gotra; but I may marry a Dhanvantari or a Maudgalya or any other, all within the Vaidya/Baidya caste. Each caste has its own set of gotras; names might be held in common; so, Kashyap is found among Brahmins. The system works the same.
Now, when individuals, families or whole clans are converted, they lose caste, hence they lose gotra. There is then no more restriction in marrying outside the gotra. However, what tends to happen is that even though converts have lost caste and gotra, they tend to marry within the former caste, treating it like a tribe. So a Muslim Bhatti will try to marry another Bhatti, but not to any kind of rigid extent; it becomes a preference, not a rule. A Muslim Jat will try to marry another Jat, but it's not a big deal. Among Muslims and among Sikhs, anyone can marry anyone else. Having said that, the preference thingy can get extreme; so a Jat Sikh doesn't get married to a Khatri or to a Mazhabi. Some Khatri families are valued and distinguished above others, since they are descended to one or the other Guru, and Jats have no problem marrying into those.
Very broadly, the gotra and the caste are gone, only the memories of the caste remain as a tribal identity (quite bogus, par dil ko behlane ke liye), and people marry within their tribe. No formal restriction, however. Nor among the Sikhs.