...who di you say you work for? 
There are two possibilities:
1. The part is the wrong size and would not fit any truck of your year.
2. The part is the right size and the opening in your dash is too small.
The vendor sent you a second part and it did not fit?
I'd try another vendor for the part. I'd try to get the first vendor to pay return shipping.
If someone else would report success or failure with this part (from this vendor or another vendor), there would be more of a basis for making additional speculation regarding the part and/or your truck.
I have ordered from Chevs of the 40s several times and have received good quality and service. When I purchased the wrong part, they readily took it back for full refund; and, if it was their mistake (rarely), they paid the shipping.
