Re: ISO: Trim rod end cap tool??
measure the diameter of the holes then go to
McMaster-Carr and search for "adjustable face pin spanner wrench". Pick the adjustable wrench with correct size pins. McMaster will sell you a new armstrong for about same price as you can find used on ebay. If you need instant gratification, then go to sears. Sears used to stock the Armstrong wrenches for $20-$30. Use heat to soften the seals and the cap should come out with only minor application of mallet.
You do not want to use a lawnmower or grinder tool. They are basically a stamped piece of sheet metal with a couple of heavy duty pop rivets. They will flex before getting enough torque to remove cap. You will end up with wallowed out holes and the trim cap still stuck in cylinder. Yes, I know, you're thinking that you might be able to use a bench vice and grab the edges. No, not really. About half the time you bend the cylinder and get to buy a whole new $1200 trim system.
a used ebay tool. . I'm guessing 1978 trim cap should be 1/4".