Inliners International Forums General Discussion Blown and Injected Here is a Holden 6 turbo project.

I believe the upper sq. ports are the intake and the lower round are the exhaust ports.

The Duggan head and block were made in Australia as race engines.

From what I have read there are Holdan blocks of different dimensions, known as Blue, Red, Black series engines.
I think one of these are the same dimensions as the US and Brazil 250/292 engines.

Harry