The Gunze Sangyo PT-50 is one of the best running models out there once it's trimmed.
As for retractable foils, they are very problematic.
Retracting isn't the real problem. The type of foils that retract are inverted "T" foils, and they are
inherently unstable. The real boats had computer controls that managed pitch, yawl and roll.
These were controlled either by movable trailing edges, or on later models, by bleeding air over
the wings to reduce lift. Controlling such a boat requires a gyro, and the most successful builder to
date, is Takahashi Yoichi, in Japan. (the foils do not retract, but are fixed)
Another issue with retractabl foils, is that the foils have to lower, , contact and seal the water intakes
from the lower end of the strut, to the Jet pumps inside the boat. However this is a minor problem
compared to actually getting enough thrust from your pump, and running stable on the inverted "T" foils.
Aimee