What is the model number? Should be OK if it's a standard SATA type hard drive. Some of them have proprietary interfaces that can be removed sometimes.
Just like og said. If it's a standard SATA drive inside the external, it should be fine.
It's just a laptop hard drive inside of that external enclosure.
im running on one right now a seagate 1tb external i took out as long as it is stata your good all i had to do was do a hard reformat before installing the os or it will it wont detect it as an internal drive