Back in 2000, I used one year of Great Lakes 3rd Mate and First Class Pilot time to upgrade to Inland Master AGT, then 2nd Mate Oceans and Master 1600 tons. This was before STCW, but if you already have 3rd Mate Oceans with STCW OICNW then I would imagine you would be ok.
Below is the USCG Checklist for Master Great Lakes and or Master Inland
Sea Service Requirements Reference:
360 days of service as Mate or FCP while acting in the capacity of 1st
Mate of GL vessels over 1600 GRT,
720 days of service as Master INL vessels over 1600 GRT, OR
360 days of service upon GL while holding an Officer endorsement as
Mate or FCP of GL & INL of vessels over 1600 GRT, OF WHICH:
180 days of service as 1st Mate, AND
Service as 2nd Mate accepted: 2 for 1; for a maximum of 180 days.
360 days service as FCP (other than canal & small lakes routes) or Mate of
GL or INL steam/motor vessels over 1600 GRT, OR 11.435
720 days of service as Wheelsman or QM while holding a Mate or FCP