The Maulerfiend, being a Chaos Model, might be a better start, especially considering it is larger than a Dreadnought:
Image credit to Thor from Creative Twilight
The Maleceptor might work, if you were willing to put the Time and Green Stuff into turning it from organic to machine.
The thing is that a Maulerfiend is only £7 cheaper than a Slaughterer, so I assume that you basically just want a model that is more unique to you? Which is fantastic, and can easily be chalked up to Chaos being, well, Chaos.
Defiler Legs could potentially be too big, so maybe the smaller legs from the Necron Tryarch Stalker model might be a better, closer to original model, bet. But as its your own conversion, the Defiler legs could easily work
As an aside, try and break up what your posting. Walls of text make for a dull read
But regardless, good to see you snooping around the forum again