funllbb- can you post a picture of what you are describing? I have a BGW 500D that is very similar to the 750 A model, there are some metal can type driver transistors in wells with compound around them on my boards. I know later 750 models went to plastic body transistors. The outputs are metal TO-3 in all of them.
Sorry I can't do pics. I'm new here and having trouble even figuring out how to navigate! Thought I'd get an email to notify me of any activity in this thread-nope! I suspect the 500 is very similar to the 750 as it was it's predecessor. I have an idea what your drivers (actually probably pre-drivers) look like. I'm betting if the heat sinks are the same they just have different boards, and a slightly smaller power supply. They look like good old amps though!