You can use this schematic, but you will have to adapt the pinout.
First you must measure the voltages of your 20-pin connector.
1. Remove the jumper block and the CPU
2. turn on the machine
3. measure with a voltmeter between ground and the pins to determine which ones are the 5V input pins
4. measure between one of the +5V rails of the PSU connector and the pins to determine which pin(s) are ground potential (you will measure full 5V there)
5. If you´re lucky and measure with an ohmmeter (machine now turned off) between the remaining pins (that are NOT 5V and NOT ground) they are all connected = 0 ohms. Then these pins are 3.3V output pins.
I just made some similar VRMs here:
What´s wrong with this FIC 486 PAK-3 ??