I'm only against headers when the cost to benefit ratio comes up short.
Headers have several operating modes, and by themselves, on a lo-perf engine, offer very little benefit in the rpm and speed range, of SOME combos.
The stock 2bbl cam IIRC is a 240/248/111+4
That means the overlap at .008 is just ~22degrees; not enough for the headers to make any meaningful power with, and even if it did, it wouldn't be until way up in the rpm.
So that leaves just inertial tuning. And this also works lock-step with rpm, but more so with throttle opening, and even more so with Effective cylinder pressure. That means, for a cruiser, operating below say 2800 and almost always at low throttle openings, nothing significant is going on; they are basically acting just as a large, free-flowing exhaust system, reservoir.
Now if you have 2.73 rear gears, then 2800rpm in first gear is ~33mph; so below 33mph, the headers are not helping you much if at all. If the tires don't spin, then the same goes for the 4bbl; the stock 2bbl is plenty big enough at 2800. If the engine can only pull 230 cfm at 2800; then the engine does not care at 2800 rpm how many barrels are feeding it, it will make no more significant power with 8 as with 2.
At or below 2800, the only things that can liven up your already-built, normally-aspirated, stock-cammed 273 engine, are; Stall-speed, and gears.
This is because at the stock stall, at WOT, the 273 make very little power, and the 2.73 gears keep the engine down in the low-power zone all the way to 2800=33mph
Just as an example, 5.38s would hit 2800at 17mph.
But the bigger deal is the stall. I don't know what your combo currently stalls at, but I would be surprised if it was higher than 2000. At 2000, I would not be surprised if your engine made only 130ftlbs of torque at sealevel. that's ~50hp. But by 2800, she might be up to 100hp. So if you installed a 2800TC, you would be looking at about doubling your available power at zero mph.This is far far more effective than headers or a 4bbl.
Now lets look at gears. Mopar's line up looks like
2.76-2.94-3.23-3.55-3.73-3.91-4.10-4.30 the splits from 2.76 to 3.55 are about 9%, and thereafter are about 4.75%.
What that means to you is, whatever torque is coming out of your transmission, by the time it gets into the rear axles, it will be multiplied by whatever your rear ratio is, or increased by the percentage steps.
Your A904 has ratios of 2.45-1.45-1.00 .. So whatever torque is coming out of the TC, the trans will multiply it by one of these ratios.
Your TC has a hydraulic multiplier inside it that multiplies whatever is coming out of the crank to a higher number that is constantly varying between about 1.8 to 1.10 depending on; LOAD/throttle opening, rpm, and roadspeed.
At 2000, earlier I said your engine might be making 50hp. This is equivalent to 131 ftlbs. So at ZERO mph, that 273 slamming 131ftlbs into the TC.
Out of the TC might be coming 131 x1.8=236 ftlbs.
After the trans; 236 x2.45 (first gear)=579 ftlbs.
After the rear gears; 579 x2.76=1598ftlbs, and as you may know, this is at sealevel, and it is a pretty small number.
Lets work it out with a 2800TC and 3.55 gears.. First I convert the 100hp to ftlbs at 2800 and I get (100 x5250)/2800= 188. then ;
188 x1.8 x2.45 x3.55=2943.. This close to double what what you might currently have and, is high enough to start the tires spinning. But recall that this is at zero mph. As the car picks up speed, the TC multiplier is gonna roll back closer to it's final multiplier which at WOT might eventually diminish to 1.1. But at say 3600, I'm imagining he torque has dropped to 165, and the multiplier to perhaps 1.4, so now, out the axles looks like
165 x1.4 x2.45 x3.55= 2009 ftlbs. So unless your tires are skinny, they will not likely still be spinning. That's ok tho, because 2009 is still ~26% better than 1598.
Lets go to 4200 about where the stock cam peaks . I'm imagining 160 ftlbs ans 1.3 Multiplier so
160 x1.3 x2.45 x3.55= 1809, still over 13% higher than the best current number.
If you had an A999 with ratios of 2.74-1.54-1.00, then it would be 2.74/2.45= plus 11.84% higher, so; 2023@ 4200; which is a really good number for a streeter.
But Ima thinking, with the A999 you could roll back to 3.23s for 3.23/3.55= 1840. And now you are cruising 65=2670@ zero-slip, in loc-up.And your starter gear is 2.74 x3.23=8.85, pretty good for a streeter.
So where do headers and a 4bbl play into this?
Well, because we are now at ~100hp @2800, the 4bbl could begin opening about here. And the power is gonna peak at say 4000, So we have 1200 rpm, and the power increase will go from zero @2800 to say; I'm guessing, 12hp at 4000, so that looks like 1hp every 100 rpm and the headers might do the same. Well that might be a lil generous for the stock cam.
But the point I wanna make is that the headers and 4bbl together will not make half the poer that the Hi-stall did, and they are doing at the top of the powerband;
Whereas the stall and gears are doing at the very bottom, as soon as you nail the gas.
Now hang on a sec; I just gotta say; 4500rpm with an A904/3.55s is now 29 mph. With the A999/3.55s it is 26mph
whereas with the current A904/2.76s (guessing that is what you have) 4500 is 37mph.
So the 3.55s have blasted thru first gear at least 12 mph sooner. That means the engine has delivered it's power that much quicker, which means it took less time to get to 29 mph, and it will also take less time to get thru second,for the same reason.
And; we haven't even opened up the engine.
