I recall reading somewhere that 1-5/8" was the ideal diameter for the primaries on longtubes for a 5.9 Magnum (but don't ask me where).
Working with "what's available", means compromises... and you still have to use complimentary mods to get the best out of any one item.

 

What's "best" depends on what you want out of it. The larger primaries will move the power band up a couple hundred RPM..... The smaller diameter tubes will keep it down low, where I want it.

 

Would also be more appropriate for a 5.2...

 

I loved my JBA shorties, I did lose a little low end but the midrange was very nice. Even in the most technical sense there is some back pressure. As the gas is pushed past the exhaust valve and into the manifold that area is occupied by gas exerting pressure "X", now call the pressure coming out of the head pressure "Y". As Y meets X, X will push back on Y. But since Y is a higher pressure it displaces X farther down the system where X piles into another pulse, and another, and another, and another, til it exits the tailpipe. Now there is a huge number of factors affecting flow. One of these that is commonly utilized it scavenging. Simply put as air passes an opening it creates a vacuum. Thus as a pulse passes by an opening where a pulse is coming down (think the collector and individual port in the manifold) there is less air pushing back and resisting flow at this point and a greater pressure difference is formed allowing the pulse to travel at a much faster rate but at the same initial pressure. Think wind here, the greater the pressure difference the fast the air moves. Heres a good video:

 

Direct fit we only have Pacesetter. LA block 318/360 headers bolt up no problem you just have to have a Magnum block gasket. The problem comes into clearance by the starter and driveshaft, but nothing a hammer can't fix and MotorTrend proved header bashing doesn't affect power numbers
Best of both worlds....http://shop.dougthorleyheaders.com/c...ers-thy-630y-c
DougThorley Tri-Y, 1-5/8" large primary tubes in a longtube configuration but being a Tri-Y they act like both a longtube and a shorty. Know a guy that just bolted some in a 95, claims they're a little close to the firewall but nothing dangerous and about 1" or so of clearance between the collectors and frame rail. Yeah the old "this guy knows a guy that did it" thing but figured I'd throw it out there.

 

The part missing on the doug thorley headers is: Reasonably priced. I am not about to pay 800 plus bucks for headers on my 2K dollar truck.

 

yeah....I didn't look at the price....nvm lol

 

I suppose that's what we get for liking trucks that have ran out of market support. If everyone and their cousin were making headers for these still, they would be MUCH cheaper.

 

That $800 is for coated headers and Y-pipe... if it's good quality and lasts, that's not too bad.
Power upgrades do cost $$, no matter how you get them.
And as I've said before, for what a new truck costs, you can do an awful lot to a 2nd Gen.

 

I tend to look at it from the "what would it take me to replace it" stand point. A new truck will set me back about 30 grand, so this truck is worth 30 grand to me. Now I know I won't get that in a sale, trade in value or insurance claim, but it makes me warm and fuzzy. Hehe