Roll bar bolt holes

[rads42]

I've done some searches and can't find this topic elsewhere although I can't imagine it hasn't been covered. Anyway I just picked up a '71 Blazer and it does not have the roll bar in it. I'd like to add one and I was wondering if the holes that it would bolt to were built in to every blazer and the roll bar was simply added at the dealer or if I would need to drill and tap new holes to add a roll bar?

Thanks in advance.