If it were me , I would source all the clutch parts , from some place that will let you return them if you get it apart and it is not the clutch . Maybe locate another transmission , if it is needed .

With the engine off , can you shift the transmission into 1st gear ? Then , start the engine ( CAREFULLY ! ) . If it trys to take off , with the clutch depressed , then I would say it is some sort of clutch problem .

God bless
Wyr