Help! My head tube is to long for a double crown fork!!!!

get a taller crown?

Have you tried a ZS headset to lower the overall length? If that's not enough you'll need to get a custom top crown with more drop machined. 

Did this on my G19 to get a mullet setup. Went from a EC headset to a ZS. Problem is the new G1 most likely already uses a ZS headset. Found this comment on a quick Google search:

It’s also worth noting that folks on the XL and XXL frames are going to have a hard time fitting a dual-crown fork. The 140 mm headtube on the Large frame is already pushing it for the maximum crown spacing on every current dual-crown fork I’ve had my hands on; the 150 and 160 mm ones on the bigger sizes are going to require taller drop upper crowns to fit.

Taller crown seems to be an option (if available) or reducing fork travel to 180/190mm.

Otherwise you could contact Nicolai and ask if there is an option modifying the frame to make it fit. I met a guy running a double crown fork on an Saturn 16 MGU, apparently they modified his frame when asked, as one of their team riders was running the same setup.

I've had a nero on a large G1, hope lower headset and a slamset on the top. Was a tight squeeze to get a mudguard in, on full compression the tyre, mudguard and crown got very close.

Boxxer max stack height is 147mm, other brands don't post the max headtube length, as the variance from the tyre height means they dont want to state anything in the event the tyre hits the crown. If they stated the tyre they used and that it was ok, it would be helpful