Hard drive size means nothing - I’d replace the hard drive with an SSD to double the speed.
The MD322LL/A is a:
'''Apple MacBook Pro 15-Inch "Core i7" 2.4 Late 2011 Specs'''
Identifiers: Late 2011 15" - MD322LL/A - ''++MacBookPro8,2++'' - ''++A1286++'' - ''++2563*++''
the MD318LL/A is a
'''Apple MacBook Pro 15-Inch "Core i7" 2.2 Late 2011 Specs'''
Identifiers: Late 2011 15" - MD318LL/A - ''++MacBookPro8,2++'' - ''++A1286++'' - ''++2563*++''
Yes the boards are interchangeable.