fuel pump

i put a 54 hornet 308 in my 51 super six the original pump that was on the motor had a broken arm that rides on cam so i inquired about a replacement. i got an answer for a precision 16067. mounted it run it for about 5 minutes then it quit pumping . i pulled it, low and behold the end of the arm where it pushes the diaphram rod up had broke off. i took it back got another one, installed it.while running the pump appeared to be rocking a little. i tightened the bolts a little tighter it quit moving .pumped for a while now it quit also. i believe the arm is not correct shape . how can i find out the correct shape for this arm. can i get just the arm somewhere and swap them out. if anyone has had this problem or knows of a solution please help me out