[30 Closed Cab PU]

I am currently running a standard zenith with flow tested jets - do not have the balancing mod.. Have a rebuilt motor/3.54 rear end/no Mitchel. Gas mileage about 15 mpg, plug condition OK.

I have also tried the high boy with the 3050 K and N, did notice the idle changed slightly down (50 RPM or so) so assume there is a slight restriction in air flow, but plug condition, power, and mileage stayed the same with the filter on or off. This year am going to try the High boy with the 9257 filter. Currently do not have the filter on. I do recommend you tether the high boy to the car in case the high boy vibrates off the carb. I tethered mine to a radiator support rod. Also make sure the gas seep hole in the bottom of the air intake does not get blocked, I trimmed a small minimal "V" in the high boy connection hose to insure the seep hole was not blocked. Make sure you really tighten down the hose clamp using a socket and ratchet, I could not get mine to tighten sufficiently using a flat blade screwdriver.. Also by V ing it I was able to get it to seat further onto the carb, and have not had it fall off since.

The air balancing mod has strong opinions on both sides, needing it vs not needing it. Some say if you use an air filter with good flow like the K and N the mod is not needed. Others say not to use an air filter since an air filter messes up the carburation no matter what type of filter is used.

I do not know what to believe. So I personally may try modifying my spare carb with a Dremel, blocking the bowl vent, and drill the hole to the air intake. If things go south I will find a used or purchase a lower carb assy., and transfer the parts from the old one.
I classify this subject with "whats the best oil" debate, strong opinions. Try things, make up your mind what you are comfortable with and what works for you. It's part of the fun of the hobby.
I prefer to run with an air filter. As I said above many say it is not needed. - Personal preference.