Alpharius' base is fairly unique amongst the Primarchs. Plenty of the show dead bodies, and the results of their actions. Some are static and show staircases, or in the case of Dorn viewing a battlefield stoically. For Alpharius, he is in the midst of dispatching an unlucky foe (unlucky, because I'm assuming that he didn't see Alpharius coming. If he did, and charged, then he was going to be outgunned as a bolt pistol was probably never going to do the trick ... the bolt pistol lies on the ground next to this marine).
The first image (above) shows how the scenic base all slots together. It too me a little while to figure this out as I was rotating the smaller base around to see which rocks were supposed to slot in to each other. I thought I had it right, but there was a gap at one point in the circumference.
Slightly perplexed, I decided to instead dry fit the unfortunate marine to the base. The knee of the marine turns out to occupy the slight gap in the circumference and fill in the scenic base. I hope this tip helps someone out! Regardless, the correct orientation can be seen above.
For the marine on the floor, my original thought was to make this guy in to another Alpha Legion marine. I was going to do this by swapping shoulder pads, or perhaps a different helmet. The sculpt of this marine meant that this would be tough to do. Both the shoulder pads and the head are sculpted together with other parts. Hence, I have opted here to keep the original sculpt intact as it simply makes more sense that way. Plus it retains everything in their original condition.
About the only this that I did with the base was to score it (picture above). Here, I've simply taken my modelling knife and etched a grid pattern on the bottom of it. The reason for doing this is to ensure better bonding when glued to the citadel base. Other than that, the base is now assembled.