It's late here but I had a go at fitting some Schottky diodes to a 148GTL-DX on the AM detector.
I don't have any 1N6263 diodes but I did find some old HP 2800 diodes and these are very similar.
The results are quite interesting and there's probably something for everyone here 
First of all I tested with a decent AM signal generator for S/N with a 30% 1kHz tone from -50dBm right down to -120dBm and looked at S/N ratio on an accurate meter.
As expected, both diode types were the same in terms of signal to noise ratio across the whole range right down to 2dB signal to noise. The 1N60 appears slightly better with weak signals but the difference is tiny. Less than 1dB.
Then I tried looking at using two modulation tones 1kHz and 1.6kHz at 30% each.
I redid the tests and got the same S/N for both diodes with the 1N60 just shading it.
However, what I did notice was that the 1N60 diode detector became less linear at very small signal levels with the two tone modulation test. These are at tiny signal levels with just 3 or 4 dB signal to noise.
This detector non linearity actually makes the radio appear to have LESS background hiss if the background signal is very low, i.e. with just a dummy load fitted. In other words the demodulated output falls more than 1 dB for a 1dB change in signal generator level. However the signal to noise ratio is the same if you turn up the volume.
Technically, this characteristic with the 1N60 diodes isn't a good thing but I think I can see why some people don't like the schottky mod to the AM detector. There is definitely no improvement in signal to noise ratio on weak signals but the detector is more linear in action right down at the threshold of sensitivity.
This will mean the standard radio can sometimes appear quieter during pauses between stations transmitting (assuming band conditions are extremely quiet with very low band noise)
Some people may prefer this with medium to strong signals on a quiet band although on very weak signals (so weak they are barely intelligible) you would have to use more volume.
I swapped the diodes back and forth several times to double check all tests.
Despite the differences listed above I would expect that under normal conditions there would be little difference as both detectors appear identical if the signal is more than just a few dB above the minimum it can detect.
