Hey Paul, I haven't played either, but on the Card Whiz, being a GTB 2 player, I'm guessing the drop targets would reset when the next ball is served, like my 2 player Pioneer.  Where as the single player Jacks Open, the targets would stay down. ( deeper rulesets on the single players) Nino or Tony feel free to chime in.
Nino has a great Jacks Open resto thread here on the forum  .
There is also one on ebay at the moment ( up here in Newcastle )http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=200313777255
It has a repainted headbox, although it looks like a High Hand/Capt Card paint job, on the head.
I think there is some owners of both machines here, so they will know for sure.
ps: I wondered when you would be after another EM for the line up.
gotta love those EM's.
cheers Steve.