Russell
Here's my AU Windsor sans power steering and A/C much like you.
I had Marty Govett fabricate and locate a mounting bracket off which he bolted a GM belt tensioner.
This is the spring loaded pulley arrangement on the left side of the system. It was the only place where cast bolt holes could be accessed.
So importantly get your belt orientation correct on the remaining pulleys and work on fabricating a stock tensioner back onto the front of the block somewhere.
It took me a couple of goes to source a belt of the right dimension to fit my layout but you generally have a fair variety of size options.
Good luck.