The 475 were part of an order for 639 sets. The initial shipment was destined for the CMHQ but diverted to UK needs. In fact the UK wanted all they could get, see photo.
Looking at serial numbers there were a lot made, into the thousands. Where they went isn't reported as my date cuts off in 1945. The Canadian Army used them in Korea and post war Germany. The installation instructions for my M152CDN was dated 1961. I couldn't find a 52 set so settled for a 19 set and two C42s in rebroadcast roll.
I wouldn't mind one but I'm getting to old to hump these around the shack!