End dump trailer build/advice

Looking to haul rock (and only rock) locally part time when I'm not busy. Trying to buy/build the most efficient trailer I can to get to 85K in Kansas. I can't afford new and I can build anything, and I have no problem making a rough old trailer work. Will be pulled with a Freightliner Century with sleeper. My belief for the sleeper is it will help me with bridge laws compared to a daycab, plus my farm owns the truck already, so please no daycab advice.

My friend has a International 9400 Eagle with sleeper. Pulls a 24' Framed Tandem axle aluminum Freuhauf and can scale 80K with about 24 tons net, with almost 2' of extra room for more rock. Very handy, short trailer, I've pulled it for him at times and I'm comfortable with it.

He also pulls a 39' Frameless 10'2" Spread Axle aluminum Vantage and can scale 85.5K with roughly 26-27.5 tons net, if loaded correct. I believe my numbers are correct. My concern is having 39' in the air.

My thought is to find a 28' Frameless tandem axle, buy a wrecked 10'2" spread axle trailer, and swap the spread for the tandem, I'm sure brackets/running gear/etc will need to be built, but its just metalwork. It may be a little rough on tires when turning but I can't think it'd be any worse than some of the quad axle dump trailers I've seen run down the road. I'm sure a 30, or 32ft would work great and not be much heavier considering its a frameless aluminum tub.

I appreciate any advice from everyone, and maybe down the road someone else will read this and get information they were seeking. Thanks!