The F-117As DESIGN is what was classified...With few exceptions, they were literally built with off the shelf components.
"To lower development costs, the avionics, fly-by-wire systems, and other parts were derived from the General Dynamics F-16 Fighting Falcon, McDonnell Douglas F/A-18 Hornet and McDonnell Douglas F-15E Strike Eagle. The parts were originally described as spares on budgets for these aircraft, to keep the F-117 project secret."
The parts that were more classified, the INS, Targeting system etc can easily be simulated without compromising any secret information. As far as stealth...again, it is easier to simulate stealth in a computer game than it is to create it in real life.