From eBay:

https://www.ebay.com/itm/US-Army-Signal-Corps-R-174-URR-Radio-Receiver-Viet-Nam-era-/203727348219

https://www.ebay.com/itm/US-Army-Signal-Corp-Radio-receiver-Power-Supply-PP-308-URR-/203686027985

https://www.ebay.com/itm/US-Army-Signal-Corps-Radio-Cabinet-CY-615-URR-Korea-Viet-Nam-era-/203727354636

It seems incredible to me that a British company would tool up to make a small order of AN/GRR-5s. Is it more likely they purchased US made parts and assembled them in England or bought complete units and put their nomenclature tags on them?

Dave N9ZC