I can't speak for that particular set of headers in a G-body but all the usual problems you can imagine can happen.
I had to dimple a tube to clear my steering column and flatten one side of another tube to clear the kick-pan part of the florrpan in my truck when I used AFR heads (raised abnout .500" over stock, if memory serves) and a set of Hooker Super Comp headers.
One piece of advice- if your engine mounts are worn out replace them FIRST before you try to install the headers. Make sure everything's where it's supposed to be before you start trying to fit up a new set of headers.
Also- if you have any brackets that tie in on an exhaust manfiold bolt you should be prepared to alter that bracket as well.