Hypothetically, if I was in your shoes and wanted to change it to 6.5 Grendel I would definitely do it. The rifle didn't cost you anything and its not too expensive for the additional parts.
Buy a new bolt face, possible sell the .223 online.
Buy new bottom metal with the correct magazine, probably CDI Precision
If its an accustock I'd keep it, if not I would replace it. Probably an unfinished Stockade.
Buy a new barrel, CBI makes drop in replacements and they shoot lights out.
Instead of inheriting a .223, you just built a semi-custom rig for under $1,000. Not bad at all!