bit order the old 2nd/3rd edition marnius calgar arm if you go that route as the fist is a bit smaller... (keep in mind the new one is termie sized!)
it's a bit of a pill trying to cut off the bolter, but as long as you have a decent blade on your modeling saw, you should be okay. (took me about 15-20 minutes to cut out the power fist...)
other than that, as mentioned there's the pointy finger power fist off the new assault marine sergeant's sprue...
as for the lightning claws - go with the metal veteran set as the termie claws will look a bit too big... (you can always add on one those plastic wreaths that come on the tactical squad upgrade sprue!
)
cheers!