Alex very fine I was lucky to have both of those with many test fixtures and plugins, since 1980s.
Amazing units, we used the 576 very often but swapped the 577 long ago.
577 and 576 are very different Animals with different V, I and plugins.
Some special applications
Testing linear ICs
HV lamps, diodes, transistors
High current pulsed testing
Valves with adapters
useful to know your location (Russia?) and application for the curve tracer.
Typically these are impossible to pack and ship common carrier without damage to controls or CRT.
Really via car or hand carry only! I would be patient and visit some ham Radio fleas markets like the German each June near lake Contanz.
Bon chance,
Jon