Body Guns
the hellfire cannons are easy. take the heavy flamers, assemble as normal. cut off the nozzle. now take four of the chaos weapon muzzles and glue them on
UPSIDE DOWN the hellfire guns are going to be glued on the bottem of the front body upside down, so with the muzzles upside down on the gun, it looks right side up when finished. i used green stuff. they shifted when i took the picture, but i put em back.
now for the demolisher cannon
cut off the circular portion of it like so

shave off parts of the front body and the demolisher cannon so that it fits in snug and flush. and the barrel decorations like normal.
glue the cannon on, then glue the two body halves together
now to attach the tail. cut off portions of the ball thing on the back so that it will fit snug. if you used any metal in the tail (a metal gun for example) you should pin it. you may want to magnetize it as well.
Legs n claws
ok now! youre almost done.
for the legs, glue them and the claws on like normal. you will have five sockets.
1(rear, tail)-2-3-4-5(front, claws)
i glued mine in like this:
1-X-3-4-claws
with that break not in the back, it balances it out so that the tail or the claws dont make it tip forward.
why GW sucks
now when i got my second defiler today, IT HAD NO LEGS
none at all. i got two body sprues and no leg sprues. but because i had an extra body sprue, i took the extra claws and made them into legs by cutting off the blades and bottem claw like this
The Brass Scorpion 
now youre done, add in any khorny decorations you might want. i used a sheild from the WFB mounted khorne lord on mine, as well as a khorne icon on top of the gun.
this is the biggest thing ive ever built.

its four carnifexes!
a landraider and a half!
its insane. happy building, and of course never forget.
BLOOD FOR THE BLOOD GOD!!