Super League's Man of Steel and the Kingstone Press Championship Player of the Year were among the Scotland players who began their on-field preparations at the Big Fellas Stadium in Featherstone.
Scotland coach Steve McCormack had 19 players in action, including Huddersfield star Danny Brough and Sheffield Eagles prop Mitchell Stringer.
Two players are currently out injured and the overseas contingent of Catalan Dragons hooker Ian Henderson and NRL trio Peter Wallace, Kane Linnett and Luke Douglas will not arrive until the second session on Thursday, which will be the squad's final gathering ahead of Saturday's (2.00pm) warm-up game against Papua New Guinea at the Big Fellas Stadium.
Half-back Gareth Moore, who has just moved from Batley Bulldogs to Featherstone Rovers, has withdrawn with a shoulder injury, while a persistent knee problem has forced Hull KR's new signing Jonathan Walker pull out.
McCormack moved quickly to replace Moore and has handed a call-up to young Workington Town scrum-half Callum Phillips.
Phillips was already training with the Bravehearts as part of his learning experience, alongside older brother and club-mate Brett Phillips, and fellow Town star Brett Carter..
Scotland will send medical reports on Moore and Walker in the next 48 hours and request permission from RLWC2013 to replace them in the 24-man squad.
Whitehaven prop Paul Jackson is a possible replacement for Walker, having won several caps in the front row.
Scotland face Tonga at Derwent Park in Workington on October 30, Italy at the same venue on November 3 and USA at Salford City Stadium on November 7.
