Even though not a full length header there, anytime you line up all pipes so that they can blast parallel to each other in close proximity to each other you will increase power. The individual pressure pulses then can pull easily on other cylinder pipes that are not firing. The vacuum there increases extraction effect. Think of the header collector as a parallel firing gun.
I've seen one Ranger cast exhaust manifold that looked like it was a 4-2-1 type, that one might work well too.
Other than that, if the individual pipes join up at the log one at a time and spread out down the log, well that's not the hot setup. They tend to interfere with each other then.
Two different types of exhaust extraction. One is pure untimed vacuum like proper collected headers do, the other is timed according to pipe diameters and lengths. If header well made then both can happen. I've hooked up a vacuum gauge to a header collector to have it show constant up to 10-13 inches Hg. of vacuum at steady cruise on a street car. So much for 'necessary back pressure', which is a myth.