This horn is not a Yuichi Arai A290, neither a TAD TH-4001, nor a Rey Audio RH3 but takes design cues from the Arai and the TAD. 

The Arai with its 2" throat (Ø50.8 mm) is not specific to the TD-4001 (Ø49.2 mm). Both the Arai and the TAD were conceived in a pre-CNC era. Without CNC the Arai is very hard to build and requires patience and a lot of hand sanding to match the curves of the sides with the main lobes. The TAD which had to be built in larger numbers used thin curved plywood sides to makes this process easier. 
With CNC things are still quite involved but some compromises can be avoided.

The TAD and the Rey-Audio are typical monitor horns. Their throat 'pinches' quite a lot and their fins are only 38 mm tall. The Arai has taller and straight 50.8 mm throat and fins. My horn splits the difference with a 49.2 mounting plate and a throat pinches only a little bit (to an undisclosed fin height :) One design isn't better than the other but more or less suited to a listening distance and room acoustics.

The construction of my horn is very solid, it is almost twice as heavy as the TAD. Dowel pins registration helps precise glueing but also prevents the splitting or wrapping of the smaller plywood parts. The sides are reinforced further with vertical boards.

This one is a Arai A290 done entirely by hand with router templates

This is my final horn, the throat is 49.2 mm and the fins are smaller than that of the Arai.

My first project was to make an Arai A290 by hand. In the following links I have detailed the different steps of the construction.

Part 1 > Drawing and Templates.