You could order the 409 in only full sized cars and trucks. Odds are the motor you have is based upon an old truck block as there are precious few passenger blocks surviving (The motor makes more power than the passenger block can contain and it often cracked the main webbing. Truck blocks were made with higher nickel content with thicker main webs and have survived when passenger car blocks gave their all).
The casting numbers will give you an idea of the intended application and year they were cast. Check with Mortec.com to decipher what you have. Back in the early sixties they didn't stamp the blocks with the car's VIN (sequence number).