Over 40 years ago, I pulled a Royal Crown trailer just like that, well almost, all over creation. At that time I though about making a model of the trailer I pulled. Mine was a Kinnard model not a Hackney,
So I sat down and wrote a letter to the Kinnard Body Works, told them who I was,that I pulled one of there trailers and what I had in mind.This might work to day with the Hackney company, couldn't hurt. Side loaders are getting outdated through. If you have a soft drink or beer distrubutor near you, go ask if you can take pictures of one of there side loaders, can't hurt and you could get the pictures you need to build one.
It was about 3 weeks to the month that a big fat envelope came in the mail. When I opened it up what a surprise, There was a complete blue print to one of there 16 bay tandem axle trailers. The exact one that I pllled every day.
Never did get the trailer built, but still do have the blueprints around someplace. I think there at my sons house, as is 1/2 my model stuff. borrowed but never returned till I find it missing and ask if he has it. Have to keep my stash under lock and key or they will drive out under one of the sons arms.
This thread really peaks my interest in something that has been on my mind for a long time. Going to have to go searching and see if I can find that blue print.