I've ordered some fitting kits for the Duratec from RetroFord in the UK. Before you laugh and criticise at least they fit and the full kit will be in the region of $3,000 x Sydney. Do the sums and call me

I have also sourced a type 9 5 speed kit which will take your big power. I will check with the manufacturer if it will take your desired 400 HP but it will certainly take the 8,000 rpm range.
These gearboxes are not available from 'Steve the engine builder' and are a specialist bit of gear. The biggest bonus is they are helical cut so no noise.
These gears have been developed with the Duratec user in mind. The gear tooth profiles are much larger than Ford original spec and are similar to a typical S/cut gear.The amount of engine torque this gear kit can be used with is about the same as a typical s/cut gearset. The gears are cut to an angle of 25 degree's this means there is more than one tooth driving at any one time which is stronger than one at a time as in a straight cut gearboxes,and also 95% quieter. They are also gear shaved after gear cutting to perfect the gear form. First and second gear are bored out larger than standard which saves weight and are fitted with caged needle roller bearings to reduce friction.
They also feature a lightened gear train, the benefit of this is enhanced syncro life and a potential faster gear change.
The gear ratios are as follows 1st 2.482 2nd 1.61 3rd 1.225 4th 1.1 5th .87 or .82 The .82 5th gear pair have an increased helix angle and finer pitch teeth for quieter cruising.
Trust me, with a straight cut box on the street you get very bored with it very quickly.
They also utilise a bigger bearing on the layshaft. No needle rollers here folks, and that's why your Quaife won't do 7,500rpm+.
Expected price? Around $3,000 without bellhousing or shifter. We can supply both.
Stocks are expected here August and orders are being taken now.
It may not be a Tremec or TKO but will fit into your car easy and parts to convert/rebuild are plentiful.