Adjusting power supply voltage
 

I have a Powermax PM3-55 power supply, rated at 55 amps and 13.8 volts dc. I wish to use it as a regulated 8 volt power source for operating my MMS Complete in the Run mode for checking rpm and amp draw. My electronics knowledge is outdated and limited at best. Can anyone tell me of a quick and dirty way to make this happen? I was told that Castle makes a programmable Pro BEC rated at 20 amps. I do not have any idea of amp draw, but could this be the answer?

Many thanks!!