It is a Stuart hand pump. Their 1/2” diameter ram pump. The one in your pic is a 3/8” pump. Look in the “built” category. I had a PM Research, 3/8” hand pump, that I built, feeding the boiler, but that is much too small to feed a 504 boiler. The 1/2” Stuart pump did the job well.
I oiled lhe ram and it did no good. Then I sprayed Kroil penetrating oil on the ram an pumped it and the ram loosened right up. I think I will bring the rivets off and pull the ram and use the waterproof grease. Thank you. That is a great idea. Does the grease attract dust or dirt outdoors at a steam show or rally?