Here's a size comparison with an E:A Revenant. The Guardian is on a lower base, but it's clearly shorter. Also a little stockier, I'd say. The worst part is probably the leg positioning. Doesn't mean you can't do it, but it'd take some work.
I don't know how tall 40k Wraithguard are - probably too tall, but the shape is better. Otherwise I'd consider aspect warriors (better positioning, less similar torsos). Not Swooping Hawks because they're one piece with a gun across their chest, if I remember right.
