Fred Copeman in his autobiography Reason in Revolt refers indirectly to the tools related to his anti aircraft lecture as mentioned by Merriman:
I concentrated on the Lewis gun, easy to handle and very light, and I knew all about. In the end, six of these guns were made serviceable, and either by design or by accident, I found myself in command of a small anti-aircraft unit….. The Lewis gun section soon became efficient. An old trick was to throw tin lids into the air from the trenches, the gunners having to hit them before they touched the ground. No small feat this, and yet every No.1 gunner within three weeks was able to hit the lids two at a time in the air.¹
“Cox” is very likely Thomas Cox Jr.. He was born in Douglas, Alaska, and was a Native American. At Jarama he was in one of two trucks that accidentally drove into the enemy lines on February 16, 1937. Fifteen Americans and one Canadian were killed, and only one wounded prisoner survived, but had his throat cut by a band of scavenging Moors that night. Cox arrived in Spain on January 23rd 1937.
“Givney” is John Givney, of whom little is known at present. http://www.alba-valb.org/volunteers/john-givney
¹Fred Copeman. Reason in Revolt. Blandford Press, 1948. p. 81.