Born and raised in this country before emigrating to Australia as youngsters, the pair have spent two months trying to get themselves classed as a homegrown players.
With no English Super League club allowed more than eight Federation players next season (meaning they must have come through the Academy ranks at an English club), becoming a 'non-Federated' player would improve both players' attempts to earn new contracts for next season.
But they have had no joy with the game's ruling body and solicitor Chris Caisley, the former chairman at Bradford Bulls, has now taken up their case.
Torquay-born Henderson, who has spent the past seven seasons in the British game, four at Cas, said: "I'm trying to get off the non-Federation quota because I class myself as a British-born player but they're saying to be one I must have played one season at a Federated club between the ages of 16 and 21.
"I can understand that the RFL want to cut second and third-generation Brits coming over, who are basically Aussies with a bit of ancestry. But I find it tough when you're born and raised in this country. We didn't want to go down the legal route, we just wanted some special dispensation on our birthplace."
The RFL relaxed the rules last week and any player on a club's books before last June is now exempt from the restrictions. But it does not apply to players attempting to win a contract with a new club.