basic GPS question for my GPS 72

I am trying to put some waypoints from a 4WD book i have. Can someone explain the following points to me...

Zone 50J??????

373 142mE 6 521 116mN??????

I'm guessing that the m in the mE and mN is magnetic north and east right? but as far as the coordinates go, i'm tring to put them in my GPS and they appear to be in the wrong format. The choices amongst others in my GPS 72 are;

hddd mm.mmm----------hddd mm ss.s--------hddd.dddd....
which is the correct format to use? What about "north reference" is "true" right or shoud i use "magnetic"??

Which one should i use to be able to enter the above coordinates?

cheers
mike