would these 2 parts be interchangeable? We have an application which uses LT1083CP-5, but we can only find the part available as LT1083CP with our distributor.
LT1083CP and LT1083CP-5 are not exactly the same.
LT1083CP is an adjustable version (you will need 2 resistors on ADJ pin to achieve a desired voltage: indicated on the typical application on the datasheet page1)
While LT1083CP-5 is a fixed version with an output of 5V.
By the way, LT1083 is already an obsolete part and is not recommended for new designs.
If you wish to use a new part we recommend to use LT1084 instead as an alternative.