AC 23-629 is the reference. Done in conjunction with appropriate analysis so the crew have some idea of the critical condition. We (myself associated with analysis so on the ground) used to estimate the start altitude so the dive would get as close as it could to what we wanted.
I recall we had a chart of achievable max IAS vs altitude in the report. The reason why the FAA warns of modifying aircraft with more powerful engines is because you’re going to get outside what had been demonstrated originally.