Razorbacks make for easier conversions... but by piling some extra armour on the front of the Rhino, you could represent the higher AV on the front of a Chimera. A little battle damage to the sides could indicate a weakened hull.
From there, assuming you're going for a "Chaos-y" feel, you could have a roughly cut hole in the front, with a Heavy weapon poking through to represent the hull weapon, and a guy with a big gun in the cupola area of the Rhino could represent the turret. A man-portable Multi-laser would be a
fluff stretch, since they're only available on vehicles normally, but if you're cool with a Heavy Flamer or Heavy Bolter turret, fluff is a non-issue.
I'd thought about using a "looted" Chaos Rhino for a Chimera, in the previous incarnation of my Guardsmen, and even started work on it, but never finished. I decided my boys looked too much like the rebels from Hoth for my liking, and I started to repaint them in Cadian colours.
I think it could be made to work quite easily.
As for the Raiders, you could turn them into Russ variants with weapon swaps and by adding a turret or something...