Go ahead and search for the bit on ebay, man. You'll be so much happier with how it will turn out.
But it depends on how your dread is modeled. The blood angels have it pretty good with their halberd thing on the normal dread body. But putting a big sword on the body dread can look weird. There's no easy way for the dread to swing it.
Put it on one of these bodies and it looks like a mini dreadknight.
The entire doomfist can fit on the dreads arm, however so it CAN look good.
The wraith swords can fit well, but the curved and light weight of the blade looks very different from the angled imperium swords.