Looking at ebay RACING MANIFOLD HEADER/EXHAUST GRAND PRIX/GTP/BUICK REGAL/IMPALA/MONTE CARLO 3.8 | eBay

Need 2 - 2.25" band clamps
Need 2 - 3.0" band clamps
Before the install should I get a better flex section, I read some leak?
Do I need an O2 extension?
My car is not lowered but will be, will the stock SD downpipe get all smashed up?
What do the lowered guys do? Get a shop to fab something else?

I am hoping the install will be much easier while I have the SC & LIM off?