Hey Steve,
Is you 67 fully stocked? What's your bioload?
Here is the air draw figures and footprint for the skimmers that you have in mind:
SRO: 570lph 9.5"x7.5"x20.5"
SWC: 650lph 9"x7"x20.58"
Avast: 800-1000lph w/ a psk-1000 9"x10"x22
I looked into the pegleg early last year and they have a video on how to build the skimmer step-by-step. Also, the pegleg w/ a psk-1000 might be overkill for your tank depending on bioload but you could always put on a psk-600 which would bring the air draw down to around 650lph. Reef Octopus also makes Diablo 160XS which uses the psk-600. The Diablo isn't a cone skimmer like the skimmers that you have listed but a typical cylindrical skimmer.
The person that first ran with scissors ruined it for the rest of us.