Chaos Bikers (part one)

Recently I have been playing a lot of Chaos and one of the units I wish to utilize more are my Chaos Bikers. The unit that I have, for the most part, are 2nd hand. Actually, 3rd hand and probably even 4th. They had quite a few owners before they ended up being mine, and as a result, they are in a rough state. One previous owner had intended them to be aligned with Nurgle, and even went so far as to add specialized metal Nurgle shoulder pads to them. I have done nothing more with them over the years other than play with them, with the lone exception of a single biker that I have painted in Slaanesh colors. And he's not even finished! (Well, was finished-off in the pic below, but in a different kind of way).

Mine are the ones on the right. 

Now that I have been getting in some games with my Khorne themed army, I have been looking at this unit, and trying to figure out what to do with them. It just so happened that I also have an unopened Chaos Bikers boxed set as well. I like the Black Legion, and I really enjoyed their Codex and thought about painting up some generic Chaos Space Marines and Terminators to go along with this army. It occurred to me as well that the Black Legion option would make sense with the the bikers as well. I can paint the squad black, but with the 3 extra bikes I can paint up each of them as the Aspiring Champions of Death Guard, Khorne and Emperor's Children respectively. The Aspiring Champion with them will represent whatever Mark of Chaos that I choose for that given unit. 

For example, If I give the Chaos Bikers the Mark of Khorne, this will be the Aspiring Champion to lead them: 

Using bits from Khrone Juggernauts.

I really think these bike look cooler without the farings on them. They look like they would go faster to me. And since this bike is going to be red, it should look like it's going really fast when i am through with it!

Another WHFB Khorne warrior head. These look great on marines!

Fitting the rider onto the bike. 

I am stumped on what to do with his left arm. Holding a weapon of some sort? Probably, but which one? Ah, options...