BGW 500R?

I came across one of these and it seems to be a very rare model from the company`s early days. From what I can gather, there were 2 types of 500R`s made, a 500 and a 600 watt version, both dual mono designs produced around 1974.
This particular amp is the 600 watt model and has a 4 rack unit model 750 face plate with a power switch and an indicator. On the 500 watt version, it too has a 4RU face plate but with asymmetrically spaced handles and only a pilot light. The power switch is mounted on the rear, right hand side.
This 600 watt amp has a bridging switch (broken) retrofitted on a plate in the place of the power switch.
Was this a precursor to the first version 750 I wonder.
In any case, I`d appreciate any other information someone might have.
Happy New Year to all.
 

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