I was just checking out my friends this week with the idea of copying it. It is a basic box shaped design with thin walled round tube on each side so that you can switch directions.
Looked like maybe 2.5 feet or 30 inches.
edit: If it’s a diy project, why not use half inch plate with beveled edges instead of those sheet feet that they build them with?
Pretty sure if you search in the conditioning forum there is a bluprint of sorts someone posted, year or so ago.
I just made mine by eye, I measured the width of my wife’s hyundi(so it would fit) which I use to get it around and went from there, imo it doesen’t have to be exact. If your old boys a welder he should be able to figure it out by a photo, that’s what I did.
Good luck, I tell friends it’s a cross between renting the ice with no spares(brutal) and running from the cops lol.
One think I would suggest is not welding the feet to the base… if you make them so the sliders / feet screw into the base it is much easier to replace them when they get worn. It’s probably not important for a personal use thing, but i know your a trainer and if your gona have clients use it itll get worn out a lot faster…