So I spent some time thinking up how to convert and Iron Warriors Daemon Prince. As per their mantra, iron within, iron without, I felt that it should be at the very least part mechanical. Given their proclivity for obliterators and widespread use of the technovirus, I settled upon a the concept of a seriously jacked up obliterator. Like, an obliterator's bigger, meaner cousin with a prison record.
So after raiding my bits box I pulled out a hive tyrant (not sure why I still had that, I stopped playing Tyranids years ago), parts from a maulerfiend and spares from a helbrute. After liberal application of green stuff, this is the result. I only wish I'd taken more photos during construction but the end result I think is pretty epic.
I'm thinking of running it on the table with the Fleshmetal Exoskelton relic to make it tougher, either as a Daemon of Tzeentch as obliterators can never maintain a constant form or as a Daemon of Nurgle, having achieved mastery of the technovirus.