Hmm... this was the kind of thing I paid a lot of money for the engine builder NOT to forget... the funny thing is that it doesn't look like the other plugs were changed. Just the freeze plugs.
I make a point to change all the plugs on the motors I build but you'll find most do not, they may pull one each side to make sure they get it draining well afterit is washed.
Jason is right, the hole on the driverside is for the dipstick, it just slides in the hole. The Passenger side is a 1/8" NPT thread but stick a allen wrench in the hole, I believe that is a dead/blind hole and doesnt require a plug, it wouldnt hurt however. You can go to Lowes and pick them up, or hit your engine builder back up he should have them in stock. The hole on the back rail of the block is nothing you need to worry about....
The passenger side hole was too small for the 1/4" npt plug. Does anyone have a picture of a block on that side so that maybe we can confirm what actually goes in there?
I saw another similar plug on the driver side that was smaller. Is there a smaller NPT plug that would go in there?