Great
pains were taken to reduce the amount of protuberances from the
mechanical
package into the tunnel section. The AMR-1's entire drive train and
engine
were tilted to pick those volumes up out of the way of the
tunnel. 
Exhaust
gas was piped into the diffuser, improving its efficiency but making
downforce throttle dependent leading to potentially destabilizing
balance changes on/off throttle.
The AMR-1's rear wing.
The "flap" was unusual in that there was no slot gap