that is a great looking Valiant. I have installed MPFI on the slant in the 68 Barracuda. I used a Megasquirt. For me it was worth the effort as I use the car for drag racing and I was after a performance edge with fuel tuning at the track. For a street only car, especially something a clean and nostalgic as yours, I would think twice. If you go with a full fuel return system, you will be dropping the tank, adding a return line and an in tank pump. Go with one of the circulating systems you will be adding under hood components.
Its your car but for something as clean as yours I would stay with a carb, even if you are wanting better performance.