Adding a drop axle

I want to add a axle to my dump truck (it was originally a road truck with sleeper and all). I bought the truck about 3 years ago. It has been a dump truck since around the 2000's. I would like to add the axle so I can haul more weight but I fear that will cause frame problems from the added weight. I can haul 17 tons the way the truck sits how after axle install I can get 19 tons maybe more just depends on how much extra weight I add to the truck. its a 1988 Westernstar 4964F single frame about 5/16 thick currently.

 

Looks like 10.5 inches I have been doing a ton of digging into truck frame and double frames. I have attached something I found interesting. I thought a double frame (that was considered a full double frame) would be from the back to front (back of the front leave spring hanger) but according to this I guess not. I also want to add that is has a neway air ride and a set forward front axle.

Would regular mild steel be ok to use as reinforcement? Or should it be I believe is called A36?

 

So will the current frame be ok as is or should I double frame it?

 

Wheel base is 300
Thats what I was thinking was rear suspension and in between drives and front suspension I mean that a lot of space for there to be nothing
Its got the old neway air ride

Also If I am going to go thru the trouble I will get the correct medal and from the sounds of it should be qt100

 

Well every state is different they will let me out at 59k gross my empty weight is 23,300 I wont load it that far I personally thing that's to much on 3 axles to stop. It has a 15k beam (figured that out when I put king pins it) but still has the 12k leaf springs