Differences between 456 and 550 V12?

I've read that the 456 is a detuned version of the 550 V12, although I'm thinking it must be the other way around (550 is a pumped up 456). I have not been able to find any discussion of the actual differences anywhere online. Is it just cam timing and advance? Or something fancier like variable cam timing and variable intake tracts?

Are there any tech books that go into Ferrari engine details? The 456 I'm looking at needs a top end rebuild (poor compression and leak down), and it will be tempting to swap cams and such since the engine will be apart. TIA!

Jeff