I recently replaced my engine with a 4th gen engine and all I have left is the cylinder head. It has good valves, nice surface, good cams, lifters, and springs. As far as I can tell it just needs cleaning. The cylinder head isn't even really varnished bc it had regular oil changes. Unfortunately the engine suffered from a bad head gasket and wore a pretty big scrape in the cylinder wall. Luckily I found it before it blew up the engine and cylinder head. If anyone needs it I'd be happy to ship it to you at your expense of course.
(Off topic) Wow! I'm surprised and pleased to hear that that kind of inter-generational swap is even possible. I've been pondering the wisdom of getting a high-mile 2010 or 2011, and putting a low-mile 2012+ motor into it. Someone more experienced than I am says that it's the 2010 and 2011 motors primarily that had the worst problems, and that 2012+ motors are less problematic. Does this match your understanding?