I have a 1954 235 Engine in my 210 and, since I have it apart to replace the rear crankshaft seal, I thought I would put in some new bearings. Try finding the correct dowel pinned mains for that engine without waiting a month…. I have a set of NOS TRW (Thompson Products) part number MS1690M. I looked at the Thompson catalog   https://archive.org/details/ThompsonTradeCatalogOfEngineAndChassisParts1950Through1960OCR220Pages/mode/2up  and found this information for the Chevy 235 engine main bearings:

Application                                                                                                                        Main Brg P/N

1950-1952 Cars and Trucks (Splash Lube & Dowel Lock)                                                   MS1175M

1953 Cars w/o Powerglide and Trucks (Splash Lube & Dowel Lock)                                MS1175MA

1953 Cars w/ Powerglide (Full Pressure Lube & Dowel Lock)                                             MS1531M

1954 Cars and Trucks (Full Pressure Lube & Dowel Lock)                                                   MS1531M

1955 Cars (Full Pressure Lube & Dowel Lock)                                                                        MS1690M

1955 Cars - Late (Full Pressure Lube & Lip Lock)                                                                   MS1721M

1956 -1957 Cars (Full Pressure Lube & Lip Lock)                                                                   MS1721M

1955 -1957 Trucks (Full Pressure Lube & Dowel Lock)                                                          MS1690M

1955 -1957 Trucks (Full Pressure Lube & Lip Lock)                                                                MS1721M

For Chevrolet Cars:

Changed from Splash Lube to Full Pressure Lube with 1953 Powerglide and all cars starting in 1954

Changed from Dowel Lock bearing to Lip Lock starting in 1955

The MS1531M has an oil groove around the entire shell and the MS1690M only has the groove in the upper half of the shell

My questions:

What happened in 1955 that caused the main bearings to change for less than one year? Did the crankshaft change - cross drilled mains maybe?

Can I use the MS1690M bearings in my 1954 engine?