A mule pulling a one-bottom sodbuster plow could substitute for a 4 wheel drive John Deere tractor, but it wouldn't be my first choice. A piece of hard maple and a wood lathe would be another option to make the forming die if you don't have access to a metal lathe. A male and female die set for forming the convex plug could be made that way, also.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!