JPL Horizons barycentric solution for epoch 1950 (before entering planetary region)
Goto JPL Horizons
Ephemeris Type: Orbital Elements
Center: @0 (Solar System Barycenter)
Time Span: 1950-01-01 to 2050-01-01 and Step Size: 100 years
1950-Jan-01 is "PR= 1.76E+06 / 365.25 days" = 4818 years