Following two years with Ferrari power, there has been frantic activity at the team's Silverstone base since the new technical collaboration with McLaren and Mercedes-Benz was announced.
"It's obviously very tight, because of what we've had to do. But the plan is to hit the last two official team tests before the season," Key said.
Key said this year's car, the VJM-02, had been "pretty much" fully defined by the time of the Mercedes announcement.
"It was then a case of having discussions with McLaren on the gearbox and Mercedes on the engine side as we had a new set of numbers to deal with," he said.
Absent from the winter test tracks so far, he said engineers have been busy working on accommodating the new technical elements.
"In some areas it was fairly straightforward. Some areas of the car matched very well with the new packaging requirements we had, while in other areas it was significantly different," he said.
"Effectively we have had to redesign quite a bit of the car, and starting in November, that's been quite a major undertaking."