fan shroud part numbers 340 ??? have a fit issue

I looked up that number in one of my books and from what I can find your shroud part# 2785312 is a (one year only) 67 big block fan shroud. The 68 fan shroud for a 340 should be a 2785614. There must be a slight difference in the two. You can sell the one you have (it will probably bring good money) and find a nice original 68 shroud You may even have some money left. Granted you have a water pump and timing cover that's oriented correctly you should have no problem installing the MP viscous fan unit.