Complex sentence: Neither the Cessna 401 and 402 were pressurized, nor are they particularly fast for the installed horsepower, instead Cessna intended them to be inexpensive to purchase and operate.
Split into simpler sentences: Neither the Cessna 401 and 402 were pressurized, nor are they particularly fast for the installed horsepower. Instead Cessna intended them to be inexpensive to purchase and operate.