I tried the C clamp when I replaced mine. I now have a bent non-functioning C clamp. I even tried taking the end plugs out, filling the top with a penetrating oil, then jacking the truck up, putting a long socket under the king pin, on a stump, and beating the snot out of it with a big hammer. That did not work either.
I took the front axle off the truck and had it done at a machine shop. They have a bench press and I think it cost about $20. I had purchased the king pins from one of the vendors but it would have cost the same from the machine shop. They were a NAPA affiliate.
Best of luck. If I did it again, I would have a machine shop press the old ones out and replace them professionally.
