So after talking with a friend it appears that I have just been blindly pursuing the original owners mistake. He said that the pto adapter should fit on the pump shaft snug enough that there is no wobble, Then the keyed shaft will stay in place and there is no need for a cross pin. When the pto adapter hole is too large is causes wobble which is what causes the key way to loosen off. 
So I will head to the parts store tomorrow and find the proper sized pto adapter.