Exhaust

Wouldn't 3" exhaust be over kill for my application?

You asked:
wanting the best performance from the exhaust system.

I answered;
I put a full-length dual 3"inch system on my car, with dynomax Muffs; no complaints

You can do what you want.
A dual 3" Mandrel-bent system is as close to zero back-pressure as you are gonna get. And Zero back pressure is what your engine wants. Is it overkill? Probably. But you'll never have to change it out, and no matter what you do to your SBM,short of supercharging it, you will never have to wonder if it needs to be bigger, lol.
I even ran that same exhaust on my winter motor, a stock long-block, lo-compression 318LA with a BIG TQ on it and fresh-air; and she didn't complain about it either.
Besides all that, at the time I bought mine from TTI, the price was nearly the same as 2.5s, and I'm big on bargains, lol.
Put it this way, I've never been sorry, and I've never given the exhaust system a second thought, since 1999.
Yes it was a lil tight between the offset springs and the tank, but it's in there and it don't rub. I bought the ones with integral turn-downs and hung them out past the rear bumper ever so slightly.
If you buy headers that hang below the steering, over the next twenty years, you will likely replace them many times...... Unless you drive like an old man, watch the road like a hawk, never plow it around a turn, and never jump it.. And "trust me" with stock suspension; A-bodies plow....... until the back lets go, then they are sideways and probably still plowing. lol.
Yes TTIs or Dougs might be hard to install, but well worth it in the long haul. All it takes is just one time forced over a curb with stock suspension, and POW! you nailed it. Now you are making an appointment at the muffler shop, to spend Mo money.

BTW; if you have a torquey 360, equal-length long-tubes are not that big a deal. But since headers come that way............. it is what it is.