I have super turbos on both of my cars, my 71 has a 446 and 3" X pipe system, plenty quiet for me. Try them I think your like them.
My 71 has had them for 10 years but has low miles and always indoors.

My 74 with a 340 has had them since 1988 and has a H pipe and has about 30K miles on them. I have had the car out to Bonneville on the salt and on the roads out there going 118 mph for miles at a time. I mean like wide open for 5 mile at a time., really beating the hell out of the car. Been there 3 different years and beat the car like 5-15 passes each time, that's a lot of beating.

Now my mufflers are blown out big time. They are much louder and sound like crap really. I just noticed a small rust hole in one muffler at least recently and the car has been driven in the rain and has been stored outside under a awning during the spring summer and fall.

20+ years out of a muffler? I'm OK with that and will get the same mufflers again. BTW my pipes are TTI and have not leaked at all since the day I put them on in 88, good stuff. My pipes are still good after all these years.

The headers...not so much. They were thermo coated inside and ceramic coated outside and really were nice headers. But beating the car out at bonneville burned off all those coatings and the headers turned to mostly rust. They don't leak and I don't plan to media blast and recoat them because I know how beat they are. I am getting new TTIs. The system was old and used hard before the first trip to bonneville, so bonneville is not responsible for all the wear and tear, but sure speed ed it up.