I should have said this first, but make sure that the pin is on a circuit with a rcd / earth leakage protection.  This is pretty good advise for any of us who fiddle inside pins.  If the house doesn't have them in the switchboard get a portable plug in one to protect yourself.  They cost next to nothing and may save your life, particularly if your not entirely sure of what you're touching.  Seriously there is enough voltage within the cabinet to kill, so please take this warning and advice very seriously.

Good to hear the meter and you are working.

You can probably get the meter probes into the 3P1 plug from the back with it still plugged in. If not remove it from the board and then measure.

After I wrote this stuff yesterday I was thinking that since you are going to need a new bridge rectifier you may as well buy it and install it now. They can be bought at Jaycar part ZR1324 for $5.95. Look at the one you've got and see how it is wired up. The one pin that is set out of alignment to the others, with the nick on the bridge corner, is the positive; it will go to the psu board via 3P1. The two pins on either side of the positive are the ac in from the transformer and the other terminal is the negative to plug 3P2.

The playfield is looking really good.