Welcome to Librarium Online!
a good way to convert one would be to make it from, n ork warboss from the 40k range, the one which does not have the helmet ir really stunning and all yuou need to do to convert it is to put it on a 25mm bas, change the weapons, file off any of the 40 things (necron heads and such) and make green stuff things if you want one it is really easy
but you will possibly need to make a certain place for him to go in a unit.
why not use the borgut model and switch the axe for a sheild and cut im in half at the waist if ur gon na mount him
"take my love, take my land, take me to where i cannot stand, i don't care i'm still free you can't take the sky from meee" ;- firefly
"i'm gonna grant you your greatest wish i'm gonna show you a world without sin" ;- serentiy
"I am a leaf on the wind, watch how i soar" ;- serenity
I swiped a 40K Nob for mine. Chopped off the futuristic bits, and away you go.