[400TT]

Thinking about it, we must have got a heap more space than 20-30mm I mentioned above. Boss's would have to be 70-90mm deep from memory

We ended up with a Boss that was only about 20mm thick, as you can see from the photos. It's about the minimum you could go as horn button only just clears the end of the column, even after trimming off the excess column length.

If you don't need to go as short, then cutting down something like SAAS boss would be a cheaper option. Especially if you are like slowy and pick up a bargain or already have a suitable boss for hacking. We had to fabricate as we didn't have enough material left to even think about using a cast boss. It's a bit of a squeeze to get horn wire through and leave enough meat left for it to be strong enough.

This was with a Torana column, which I'm assuming you have in your DRB...if your DRB is not one of the later generation cars.