The Fiat 124 was rebadged as a Fiat 2000 when they switched to the 2 litre engine in 1979. They achieved the extra displacement by increasing the deck height of a 1.8L and installing a crank with more stroke. The combustion chambers were opened up, which increased flow but decreased compression. In general, 200hp is about the "reliable limit" on these engines - however they have been built and dyno tested at over 300hp for pure race applications.
400hp? I say no.
Even if the guy is running aftermarket parts, the mains won't take the loading.
And running LOX? Bull****. The head won't take the combustion temps that LOX would generate, and on top of that he would have to have some seriously over-engineered delivery and metering system. Maybe (and I mean maybe) he is using gaseous ox, but you still need a metering system. It's not like just sucking ambient air. And I still think that the head temps would be too high.
Run it by Guy Croft if you really want to be sure.
Guy Croft Racing Engines Lincoln UK 01522 705222 • Index page
Personally, I think you got trolled.
He would have dumped tens of thousands of dollars into a $3000 Fiat.