This is a Version B motherboard produced from 1984. Numerous chips surrounding the VIC-II (MOS6569) graphics chip have been replaced by a single clock generator IC (MOS 8701). The locations of the SID (MOS 6581) and the PLA (MOS 906114) have been swapped with respect to Version A-CR.
The MPU is a MOS 8500 and not the MOS6510 that is usually found on longboards. The MPU is produced in week 51 1985 which is the same as most of the other chips and it does not seem to have been replaced. So this may just be another example of Commodore using whatever parts they had in stock.
All electrolytic capacitors and voltage regulators have been exchanged for new ones as described in the C64 Capacitor Mod (link).
Capacitor C38 (51 pF) has been replaced by a 4.7 nF one to make the RESTORE key work like all the other keys as described in the C64 RESTORE Key Mod (link).
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