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Can I add a 2014 MBP logic board with a discrete GPU to a 2014 15” MBP that only has integrated graphics? or is the frame and or screw holes different?

The IG and DG models are very similar! So you could swap out your IG logic board with a DG board but you will also need a new heat sink. Now the bad news ;-{ I think you’ll find a used system for less! Check eBay Here’s a price list for reference: Mid 2014 15” MacBook Pro Logic Boards Here’s the guide MacBook Pro 15" Retina Display Mid 2014 Logic Board Replacement