The GK chest plate does fit an SM body, so If you bought Helmets, Chests and storm bolter arms you could do it.
But honestly buy the time you pull all that together from bits you're probably better off just buying a GK kit outright.
Of course you could just do the bolter arms and there are always plenty of them left over.
What do you ultimately want them to look like, arms, weapons etc?
If you just want arms and flachions I'd be happy to mail you some I have crap tonnes.
You could check with Mr B.a. Kits for the chests.
Last edited by Magpie_Oz; 08-05-12 at 12:41 AM.