Lots of people do run sparks equipment, but you'll see more dual pipes because they offer comparable power with less noise which becomes an issue where db testing occurs.
As for the builds, I haven't ever looked into 700 motor builds at Sparks but I recall that the wait to get an engine built was anywhere from 8 months to over a year when I wanted my 660 done. Wait times have varied since, but can still get quite lengthy.
