I have been wanting to get a hero mounted on a juggernaut for a while but have avoided the metal kit from GW as I know too well from experience that they can be a pain to assemble if the metal parts have warped. A while ago I thought of using the bloodletter box combined with the plastic knights, buying those boxes new would come to £49! Of course I could reuse some of the parts and sell on others, luckily someone else had that idea too.
A seller on eBay had combined the kits but armed the knights with lances which is inappropriate for Warhammer fantasy. I was able to cut off one arm at the elbow and glue on a mace arm.
The second knight had his arm cut off at the joint, I was able to reposition it and cut off the blade and then attach the standard. Not sure I would use them both at the same time, and having a frenzied battle standard bearer sounds like a gamble to me.