SP started Overnight service in the late 1930s
The first was LA<>SF on the Coast route
Additional services were Oakland-Portland,LA-Phoenix, and NWP
Account higher speeds SP rebuilt SS boxcars with steel sheathing and special paintjobs, and replaced cast iron wheels with steel wheels on those cars and some cabooses.
Postwar trains used all steel [as built] boxcars and some trains used Harriman coaches as caboose.
IIRC overnigts were discontinued during WW2 but YMMV
In the 50s intermmodal took the place of LCL in boxcars
In the postwar ETTs the trains were 37x numbers as CME CMW and advance CME Advance CMW
'Coast Manifest East' [or West]
They were scheduled to get into San Luis Obispo and meet there so as to get out of the way of the Larks
This will get you started, and others will correct my errors
Hmmm it may have been an Overnight or 'Zipper' that followed on the Lark 76's yellows and rear ended it north of Paso Robles ca 1940 - Wellsona, a siding removed in the last decade or two
Wright's Daylight book has some information as should Church's 'Daylight 4-8-4s'