trainjunkie, you were very close. Per Joe Strapac's Southern Pacific Review 1981, caboose # 4239 was rebuilt by Espee in 1973 - 1975 as a C - 40 - 5, while C - 50 - 7 # 4628 was built new by PC & F in 1978. Of interest in the caboose article is the fact that the C - 40 - 5 class was built by Whitehead & Kales, who normally built auto racks & fixtures. Also, this series was the last to be assembled with rivets.