The normal bias is actually 200V for the 1967-1975 models (the SR-1 is also 200V but the very first units were 150V). The 1977 and onwards models all used 230V bias but many models still used pre-1977 drivers and worked just fine off the higher bias voltage.
A simple voltage divider off any of the PSU lines would work for a normal bias supply or any of the other bias voltages we are using (180, 360, 500 and 540V).
Mine is sitting here right now. 16kg of aircraft grade aluminum just for the BH amp boards. I'll post pics when I have some time...