I have built a 1/72 Seiran of Tamiya. I believe that Seiran is the most beautiful aircraft.
I took some photos of the cockpit before assembling.
I compared it with Tamiya 1/72 Shiden.
The kit needed weight(s) of 12g. I used metal spacers. The long one is in the head, and the others are in the leg. I do not remember the spacers’ diameter, but it may be 4mm or 5mm. The Seiran is balanced very very well.