1. Copy the .3dl file into the following directory:

/Applications/Hiero1.6v1/Hiero1.6v1.app/Contents/Plugins/OCIO/nuke-default/luts

2. Edit the following file in your favorite text editor:

/Applications/Hiero1.6v1/Hiero1.6v1.app/Contents/Plugins/OCIO/nuke-default/config.ocio

3. Look for the section in the file that specifies the display luts. It looks like this:

displays:
default:
– ! {name: None, colorspace: raw}
– ! {name: sRGB, colorspace: sRGB}
– ! {name: rec709, colorspace: rec709}

4. Add another view definition for your custom LUT:

– ! {name: LogCRec709, colorspace: LogCRec709}

5. Go to the very end of the file, and add a colorspace definition:

– !
name: LogCRec709
family: “”
equalitygroup: “”
bitdepth: 32f
description: |
Conversion from Alexa LogC to Rec. 709
isdata: false
allocation: uniform
allocationvars: [-0.125, 1.125]
from_reference: ! {src: LogC_to_Rec709.3dl, interpolation: linear}

6. Restart Hiero

And that should do it.