I don't know of any commercially available adapter plate for a M400 / M410 to T5 conversion.
You may be better off repurposing your old BW35 bellhousing with a custom made adapter plate for the T5, and then using a hydraulic thrust bearing setup. After very bad experiences, I avoid Dellows like the plague. An Exidy clutch can be found to fit the 164 flywheel.
Six cylinder Ford Australia boxes have a unique helix angle on their input shaft to cluster gear, which doesn't match up with the US-centric input shafts with the same number of teeth.
What type of Falcon T5 box have you got (tag numbers)?