3 wire 240 to 4 wire 240?

I recently purchased a welder with a 250v 3 prong plug (6-50P) and purchased a 25 ft roll of 10 gage 3 wire( ground ,hot,neutral). I also bought a 4 wire Range cord 6 gage rated at 50 amp. What I was going to do was cut off the end of the welders cord and wire in the 25 ft roll of 10 gage wire, both of these are 3 wire with the green being the ground. That seems to be simple enough, the part that I am having trouble with is figuring how to wire that same 3 wire into the 4 wire range cord, so I can plug it into my range recepticle when I need to weld some. The 4 wire Range cord has a black(hot), green(ground), white(neutral), and red(hot)?? thanks alot Danny