Header-to-muffler exhaust recommendations, pics appreciated

MopaR&D said
I have that book, it's actually what first made me aware of the importance of header secondary tuning and collector extensions. Then Engine Masters did their tests which proved it even more. I could just go and use a tape measure to see how much distance there is from the mufflers-forward but I don't know where the collectors would end once the longtubes are in. I don't really want to run a crossover as I'm tired of the sound, reminds me too much of late-model Mustangs/Challengers/Camaros.

I'm not worried about the mufflers being restrictive, they are 2.5" ID all the way through although they do have louvers which impedes flow a little bit. But my 360 would be putting out around 450 HP at best anyway. With the current setup it's closer to 400-420 HP and the shorty headers and small head pipes with tight bends is far from ideal, probably only slightly better than log manifolds.

I know having the pipes bend in and run down the center of the car then bend back outwards to the mufflers would add some length but I intend to fab it up myself from one of those DIY pipe kits so simpler is better, also would be nice to not have anything running under the transmission or driveshaft to make servicing those easier.

Season 5 - Episode 16 from Engine Masters.
It was on the “COVID 350”. It is a .030 over 350 @ 11.4-1 with AFR ported heads, single plane and a 850. Camshaft is (IIRC) 244@050.

The 1-5/8 headers liked the longest set of lengths of the collector extension in which they started out with a Summit 18” extension and welded an additional 12” pipe on for a very long extention.

Both the 30” & 24” extensions made the most torque down low and power up top.

With the pressure wave cancellation boxes, you’ll not need a H or X pipe anymore.
Your current headers are the biggest HP robbers right now.
Where ever the headers collectors end up and the pointed direction they s going, I’m sure you’ll not worry about it all.

I just suggest using the same diameter of collector to the pressure canceling box and the 2-1/2 out is OK.
If the pipe bends are consistent/ mandrel bent, that’s as good as it gets so don’t worry about it.

I have metal ready to go for this exact project. Then my welder stopped working. I don’t have the funds in the “Run account “ to replace it yet.