This is a worthy project. there has been talk of an HO kit eventually being produced, but there is no time frame specified, so if you want one, you'll probably have to build it yourself. These cabooses were covered in an article I wrote for the Fall, 1999 AC&YHS News (Vol. VI, No. 3). The cars were rebuilt from boxcars, as you say, but were actually a bit shorter than you suggest. The boxcars had a 36'0" length, and that length was retained in the final caboose configuration. They were rebuilt from AC&Y boxcars in the 500 series between Sept., 1921 and August, 1923, and are believed to have been the first bay window cabooses on any railroad. The article needed drawings, but we were unable to find any, so I drew them myself for the article. No height dimensions have been found, so I looked at photos and made some educated guesses. One particularly helpful photo showed one of the cars coupled up to one of the International Car Co. 60-65 series steel cars. Since we knew the dimensions of the steel cars, I was able to make a pretty good educated guess as to the correct height. The drawings as published in that issue are probably the best available, but I would feel more comfortable if the dimensions were more thoroughly documented. They cover two cars: numbers 52 and 54. If somebody wants to try to improve on them, I encourage them to give it a shot. The Model Die Casting old time boxcar and refrigerator cars are the right length and may be the best starting point. I don't know whether they need to be lowered, but I suspect so. If I were doing this, I would probably start with the reefer because there would be no need to fill the side door opening. The reefer has a flush door, so I would just chisel off the reefer door hardware, sand it smooth, and use a hobby knife or scriber to cut the grooves between boards. If you can't find a copy of the magazine, email me at firstname.lastname@example.org
, and I'll send you a Xerox of the article, or maybe even an original of the magazine if I have an extra. This is on condition that you post a photo of the car when you've finished.