"Opposite sides of the same coin," perhaps?
I've included time markers to jump to for those who don't want to/have the time to sit through all of the videos.
Savior Machine in 1995 (jump it to 1:30... or 3:30... or watch the whole thing)
http://www.youtube.com/watch?v=oh_Ykna-W5U
Ghost in 2011 (jump to 1:00)
http://www.youtube.com/watch?v=TMwQrL8Bf1g
Savior Machine sometime in 2006 or before (jump to 1:30 again)
http://www.youtube.com/watch?v=toUUTIg-kfY
Ghost in 2011 (jump to 0:50)
http://www.youtube.com/watch?v=DZ0HN4alZYs
Savior Machine from 1993
http://www.youtube.com/watch?v=TNA05RLojkM
Ghost from 2010 (duplicate, works here too)
http://www.youtube.com/watch?v=CaAb421KUhk
See above ^ You're right that they're not direct clones of eachother but I think there's still enough there to draw a comparison beyond just the costumes and stage show, though both of which would still weigh heavily for comparison basis. High-tuned guitars, strong drums, interchange minor-key somber goth metal/rock for minor-key somber stoner retro metal/rock, +/- religious/social context, and voila. Broken down further, the only difference I see, aside from lyrical content and vocal prowess, is a bit more bouncy drums and a little heavier guitar riffing.
This is coming off as though I dislike Ghost. That is completely incorrect. Afterall, they're just like one of my favorite bands.
Sad, but true. Breaks my heart
Yes, sir! I'm rather partial to the darker, slower stuff. Particularly the pieces from the Legend trilogy. I'll post the vids to help my case, though this one does more to disprove my point, heh. Jump to 1:20 here since the long intro was there to allow him a minute of prep for the symbolic blood staining of the UN flag.
http://www.youtube.com/watch?v=CLZVHg5GhZ8
This song gives me chills! Blood-soaked flags, chains, APOCALYPSE! (Are those drums and that rhythm
not 70's rock inspired? 2:46

)
http://www.youtube.com/watch?v=KepsB-D2zv0
And lastly, this one comes before that one ^ in the order flow of the show/symbolism, but I'm putting it last as my final discussion point for those still not convinced. I feel like playing this backwards would be the next Ghost single.
http://www.youtube.com/watch?v=c3X07mItJuw
I didn't mean to turn this into Savior Machine Promotion Headquaters. Now let's talk about
Mercyful Fate.