Sooo an update.
After ordering and opening up the Morrgryph, it became obvious that the front claws are also not "Griffon-like". Hmm. Then, when the eBayed General on Griffon (complete with superglued cork and some sandy substance all over the base) arrived, it became obvious that the back end of the Imperial Griffon is one chonky rear, especially compared to the fairly slender Morrgryph.
It was at this point I considered just selling it all and giving up on my idea.
But... Good news everyone! I am stupid and stubborn and decided to try anyway... so I started gluing the front of the AoS model together. Once that was done I roughly lined up the Griffon next to it, and sawed off it's rear end. Cue lots of clipping, sawing, swearing, chopping and changing, polyfilla, green stuff - for which my skills are limited at best - and at least one "Oh God oh God I've made an expensive mistake" moment... I think it's actually working. And amusingly half of my efforts are going to be hidden under the folded wings! Hopefully the paint job (which I'm at least passable at) will cover up some sins!
And so I present for your amusement: The front half of the AoS Lord-Vigilant on Morrgryph and the back end plus front claws of the Imperial Griffon, ridden by the Lord-Vigilant's legs, with the Karl Franz body and the Empire General's head and arms...
(Wing and the reins not pictured)



EDIT: I hate close-up photos, so just went and sorted out that uneven green stuff on the rear harness...