Hi Rado
In your situation used to jack it off the ground, fit it all together as it should be, tighten up nut; holding spanner close to the nut so as to lessen torque force.
Then back off nut 1/4 turn and attempt to fit in split pin. If it wont go in, back off nut until split pin goes in.
Loose is heaps safer than too tight. Never had any hassels doing it as above.
Cheers
Chimo