I had a bad dream, i look at a slant 6 exhaust and think , why dont use the hole in the top for something...
Put a turbo for example, it could be done. Just to fix an adapter and connect to the three hole.
And the stock exhaust flange in the bottom for a wastegate..

But were was on problem left, How to do with the intake manifold?
Look at the space between the middle intake runners at the Aussie intake..
could be enough for the turboadapter to go thru . They have a long runner intake also, even more space.
I now its an unusual place of a turbo, but there are some advantages

1 Its over the intake, you can avoid some heating problem
2 Its a good , high place for the oil return pipe
3 very close turbo - intake if you want to rune without IC
4 You dont have to fab. an exhaust header. ( and i dont think you need headers
under 350- 400 whp
5 The intake have bungs for injectors, if you want fuel injection
6 I have seven hobbies sex and alcohol.. e 85 slant 6 .....

Thomas