The G5RV is a 102 ft center-fed dipole fed with ~30 ft of 300 ohm twinlead plus coax the rest of the way to the shack.
The ZS6BKW is not a perfect antenna. The SWR on 80m is too high and the 40 ft ladder line matching section is a little too long on 17m and a little too short on 10m putting resonance outside of the privileges of the technician license. The standard ZS6BKW is mismatched on 60m, 30m, and 15m and requires a relay-switched parallel capacitor (or open stub) across the ladder line to achieve resonance on those bands. Here's what the standard ZS6BKW SWR graph looks like before modifications.
With a few modifications, the following measured SWR values were obtained from the modified ZS6BKW.
Now we will turn our attention to the next easy-to-fix problem and that is the resonant frequency on 10m which is about 28.7 MHz, 2-3 kHz higher than the tech frequencies of 28.3-28.5 MHz. What can we do to bring the resonant frequency down to 28.4 MHz? If we mount a 10 inch parallel open stub of 300 ohm twinlead about 5 feet up from the choke-balun, we will shift the resonant frequency to 28.4 MHz with an SWR of about 1.8:1 at that point. Here's a picture of the author's 10 inch stub. Because the parallel reactance is so large on the lower frequency bands, the stub can be made permanent without appreciably affecting conditions on any other band.
The following modification looks like it would have little effect on the ZS6BKW. In fact, if one wants to avoid an antenna tuner, it has a large effect especially on the higher frequency bands. It can be implemented locally with a DPDT knife switch or remotely with a DPDT relay. Note that because of capacitive effects, it can only be mounted at the output of the 1:1 choke-balun at the ladder line to coax junction on the ZS6BKW antenna system. The following device will add zero or one or two feet to the ZS6BKW matching section at the 1:1 choke-balun.
Now we come to the modifications that most hams will probably think are not worth the effort. However, in the spirit of completeness for an all-HF-band antenna, the author has designed and tested each of these modifications on his ZS6BKW and they work as advertised. The 80m SWR can be further improved to perfect (at one frequency) by the addition of a parallel capacitor on the coax at the 1:1 choke-balun terminals. Unfortunately, that capacitor must be removed for operation on the higher frequency bands and thus requires remote control of a relay (or manually lowering the antenna each time 80m operation is desired.) The following graph shows what happens with the various combinations of a series capacitor and a parallel capacitor at the balun input.
And here is how to do the switching with knife switches when one has access to the balun position as does the author. Most hams would have to use a relay (or two) for this function.
 Someone apparently misunderstood the purpose of this device and asked Owen Duffy about it. https://owenduffy.net/blog/?p=13621
The misunderstanding was apparently communicated to Owen because he complains that this is not a general purpose way to change the length of ladder line. What Owen seems to have missed is that this device was never intended to be a general purpose device. The description appears only in this article about the ZS6BKW antenna system, applies only to the ZS6BKW antenna system, and can only be mounted on the output of the 1:1 choke at the ladder line to coax junction. As can be seen from the graph, it only works for 40m, 20m, 17m, 12m, and 10m (with a stub) where the ZS6BKW antenna system is already close to resonant and on 80m only with the series capacitor. W5DXP apologizes for any misunderstanding about the application of this device. It may or may not work for other applications.