Here's the deal.
Just looking for some educated opinions.

Can go dual with existing manifolds, assuming no cracks, for around $700.
Back with stock, assuming manifolds are good, for around $400.
Have not really explored the header option.
These prices are installed.

Current exhaust is rusted to just about useless at the joints. I have temporarily welded everything together to seal leaks during driveability tweaks.

I have one yet to discover, collector or exhasut manifold. After all the fooling around under there the rust has caused some of my previous repairs to fail. So now it's time for new.

Is it really worth headers on a 305?

Manifolds and dual pipes? Will this add a noticeable improvement in power/torque? Cats and mufflers of course.

Go back stock style? The Y pipe seems in acceptable condition. The cat has been gutted, per muffler shop.

What, if any, is the most performance bang for the buck?

 

You can easily go duals, go with 2.25" pipe all the way and have an H-pipe welded in just after where the stock cats would go. That size pipe flows enough for a 305 but not too much, too large of pipe reduces velocity which in turn reduces power. The H-pipe balances the exhaust for more torque and a smoother sound. Go with some good flowing mufflers, Hooker Aerochamber mufflers sound a lot like a Flowmaster 40 but they flow a lot better and they don't drone near as bad.

 

I would say dual
You'll look better and sound better
I have a Flowmaster Super44 and I get a nice deep sound, it would probably sound even better on a v8.

 

If duals from the manifolds or headers is too much, run a single 3" pipe and use a dual out muffler and just run dual tailpipes for the look, I have that on my Sierra since it's cheaper and easier than true duals, plus it sounds just as good.