Xausa, this is a prewar commercial Mauser action, rebarreled to 9.3x64 Brenneke, not 8x64. The rust pitting is a quite common sight on German guns that escaped liberation in 1945 and were hidden for several years in the most unlikely places.
These rear scope mount bases are usually found on 1960s Mannlicher-Schoenauer GK rifles here in Germany, a typical German aftermarket claw mount system like the one on my 6.5x68 M-Sch:

BTW. the sellers name is "Bettpannenchef". I would rather translate this as "boss of bed breakdown". "Bed pan manager" would be "Bettpfannenchef".