Hello everyone.
Now I was able to install a 1400MHz P-III Tualatin processor. This required editing the BIOS (a lot of attempts before the success).
To install it, you needed an adapter PCB.
Of some tests, its performance is higher than the original K6-2-300 in 4 times. It is even ahead of some P4.
I also added preventively small radiators to the power converter.
I was surprised when I measured the frequency of the trigger restart. This amounted to 54 microseconds (18-19 kHz). This is many times higher than the one declared in the datasheet of 2 kHz. In the photo - the impulses start trigger 54845, measured using LeCroy.
Indeed, I see a lot of "threads" this device processes in real-time mode.