I have Hooker Headers and 4" Side Pipes on my 69 Big Block (454 not 427). Although the 69 was designed to be able to have Side Pipes I have to say that there is no problem with them, in fitting them or getting at Spark Plugs or anything else. I have no experience in other years though.
Two things that I will say though is; one, the noise from the pipes is gorgeous and LOUD and when you are putting your foot down whilst tooling around you get a fabulous reponse. Second, given that it is loud then it makes it difficult to travel any great distance at any decent speed. 3,500 or 4,000 revs for half an hour will be too loud and irritating. You have to decide what you want the car for. Cruising, scaring the pigeons and posing or long distance travel. If you want to travel at speed for any distance then forget the Side Pipes. Your ears will not thank you !
On the other hand letting rip from the lights is fantastic ! ! !