Don't these things seem to last forever regardless of oil used? I agree that a 50 weight is a bit excessive.
IIRC, a member here once mentioned about an old girlfriend, sister etc. that had one and accidently ran it for quite some time with no oil in the sump. After someone who was a bit more mechanically inclined heard it, the oil was checked and the dipstick was bone dry. Oil was added and the Jeep lived on.