I am assuming that your motor is pre 1947. The manual for the 1947/48 update talks about new precision interchangeable main bearing inserts so I am assuming that pre 1947 the mains were babbitted right onto the block and caps. I don't know of any conversion for this.
The rods will be direct babbitted rods and there is a conversion for them. The rods must be machined to take inserts and the inserts are specific to the application, they are not the inserts for the full pressure motors.
