This is the bsp I was using. https://etler.com/docs/BSP/512/512-700-100_I5.pdf
Is there another I should be looking at?
Nice to know it can be done. I just wondered if there was a way to derive spares off the 82b block to strap to the ac terms normally connected to the transformer.

It's probably not possible to do that with an 82b I'll have to look at more carefully. I bet it is easy with a 223 block setup