In the 1990s and early 2000s several swords were sold at hombu based on dimensions and instructions provided by Hatsumi-sensei.

All have longer than normal tsuka. Another nice thing about these was they came with extra-long sageo,

Top to Bottom: generic iaito, Kukishin iaito, Shinden fudo iaito and Togakure iaito.

Dimensions

Standard generic iaito
Tsuka:29cm Blade: 73cm

Kukishin Ryu iaito
Tsuka: 32cm Blade 76cm

Shinden Fudo Ryu Iaito
Tsuka: 32cm Blade: 87cm

Togakure Ryu Iaito (Ninjato)
Tsuka: 32cm Blade: 55cm

Measurements were taken with a tape, so they might be a little off.

Thank you to Alex Meehan for sharing the above information.