[1968 nova ss]

noticed my 68 nova ss pitman arm has extreme amount of play in it . time to replace...this is an original 68 nova ss 396/350 hp car with power steering. I had purchased the car from wayne Bushey around 1998,in which wayne had bought the car from original owner..i doubt it has ever been replaced...but the numbers on pitman arm are .I think for a manual box car..numbers read 17 gmt 3935075..center to center on pitman arm is 5 and quarter inches..is this correct ..and any suggestion on a place I could purchase a new pitman arm or good used pitman arm with the correct gm numbers... thanks in advance.Chris Teed