get your hands on a piece of 3/8th's thick 6" x 8" CRS steel. A standard 3/8" reamer and 23/64's drill bit. ( note a 3/8th's dowl will do 98% of all the rounds out there, but you can use .25" or metric ones if you can find them) You'll also need a bunch of pins to go in the holes you ream (do about a dozen holes). Turn one end of the pins down for about .004" clearence with the case I.D. (I use standard dowl pins 3/4" long) Press the pins in the plate, and your done. Goto a welding supply house and buy two welder's temp sticks (look like crayons). You want a 400 degree and a 500 degree stick. Draw a line down the body from about 1/4" above the shoulder all the way down to the end of the neck. Now lay the plate on a burner on the stove (electric seems to work best here), and crank up the heat. Mark the plate with the 500 degree stick to tell you when it's hot. You'll also need a bowl of ice water to quench the cases very quickly to stop the anneal process. Stand the cases upside down on the pins and wait for the temp stick to melt (I recommend placing them in the pins about twenty secounds apart). When the case reaches 400 degrees it's about right for the quench, and by the time you get it quenched you'll be around 430 degrees.
You can make the pins out of drill rod, or even CRS steel. But dowl pins work best as they are made slightly over sized for a press fit. Been using three plates for ten years now, and most of the parts came out of the junk pile
gary