Ive just ordered one of the ASH silicone reducing elbows for the plenum to afm so will let you know if it fits, some say it does with a bit of tweaking.
If it helps anyone else this is how the standard 80 to 70 reducing elbow fits from ASH. The bolt for the afm mount can be put back in with only slight deformation of the hose, nothing to worry about but i may make a small stainless bracket just to be fussy.