Added termination resistors?
Bingo - carefully wedged a couple of empirically selected 120 ohm resistors across the header pins.
Basically your experience surprises me to the extent that I know there's something amiss. What do you mean "across the header pins"? If you mean as a series termination resistor, then that would, of course, reduce the peak current transients thus making the decoupling less critical.
I recently built an "edge" generator using multiple 74alvc1g14 gates, which have a
much faster risetime than LS series (probably around 1ns) and a much higher symmetrical output drive capability. Each gate had its own 10nF 0603 decoupling capacitor. The circuit was one '14 as a relaxation oscillator, driving one '14 as a buffer, driving 6 '14s in parallel. Half of those simply had their outputs paralled up so that any reasonable capacitance was a non-issue. The other half approximated a 50ohm output by each gate having a 130ohm series resistor, and the other side of the resistors connected in parallel to the "50ohm" output (150/2 => 50, of course).
The overall output was extremely clean when driving either a standard 150MHz high impedance probe,
provided the ground lead was short. See the relevant oscillograms with short and long ground leads at
https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/ The signal was identical when driving a 1.5GHz 500ohm low impedance Z0 probe, and identical with the 50ohm output.
Hence I can only conclude that the lousy breadboard construction is the root cause of your waveforms.
Soon, I hope, I'm going to get around to building a homebrew 2GS/s 2GHz scope, so then I'll be able to see the edges of the 74alvc1g14