76 was the first year and it was a 400. 425 came out in 80, 465 in 81 and 82, 490 in 83 and 84.
I used to ocasionally race a 84 IT490 in enduros in 85 and 86. Did my first Blackwater 100 on it also. It had a great motor, smooth and torquie. Im on the IT site, great site!