The arduino scope + pc software is amazingly good up to a few KHz - 0-5v input range - I downloaded it free from somewhere but have forgotten where.
Can you identify the mosfets on the 4-channel board? They seem to work OK. Perhaps they are available in to-92.
This is my Raspberry Pi / Arduino oscilloscope, with a 58KHz sample rate you can measure up to about 20KHz waveforms.
Can you suggest something in to-92?
2.5GHz sampling - yep - that'd be plenty.
The 2N7000s you have might have a threshold voltage of >=3volt, making them useless for a 3.3volt level shifter.
Try to measure threshold voltage with a DMM.Connect (short) gate to drain, and measure between drain (+ lead) and source (-lead) with the meter set to diode test.You should get the threshold voltage on the meter, or nothing at all if Vgs(th) is >3volt.Leo..
That's not the threshold voltage, that's probably somewhere close to the plateau, but the current is probablytoo low for reliable value.