Chevrolet 216 235 (early) main bearings? The same?

[Lynn Eades]

Alex, I am not 100 % sure about the shims, but logic says they are left out with the precision bearings.
These bearings are made to fit a given size bore (tunnel) a part result of the factory line boring of the block when machined.
The precision bearings when paired do not form a perfect circle in this situation as they are usually "sprung" to some degree.(Is this what you have Mike?) This helps them hold in place during assembly (before the caps go on) I think this is the "nip" part of the motor reconditioner's term "nip and crush"?

These bearings also have "crush" Basically when the cap is pulled (torqued) down, the ends of the bearings at the split line are crushed together, forcing the shells into a tight fit with the tunnel bore. This is important as it stops the bearing from rotating in the bore, and it achieves a metal to metal surface contact, essential for heat transfer.
To follow on, the block bores and the shell backs should be cleaned with a solvent and only fitted when perfectly clean and dry.
BTW. the locating tab would not stop the bearing spinning and in modern engines the manufacturers don't use them.