International is okay but the best medium duty would be a L-8000 or L-9000 Ford. The Louisville has a upright seating position like a truck should. International is the same.
A F-600 is a pretty light truck it with a heaviest gvw of 29,000lbs. A single axle with a 33 or 35,000lb gvw is a better truck.
If you are 6'5" and 400lbs you need a truck with a decent sized cab. I drove a 1700 International for awhile yes it was a little cramped. I'am only 5'9" and 170-180lbs so I guess I'am average size for a guy. The worst truck is the MR Mack good god my left leg would cramp up driving that truck.
The 466 International engine is one of the better medium duty engines out there. The 1700 International I drove was a gutless 360cid engine your foot never left the floor. Shifting the 6spd you only lifted your right foot for a second and slammed it to the floor again.
Floating the transmission was the quickest way of shifting it.
The other cornbinder I used to drive was a 2600 series it was okay but I prefered the Louisville.
What ever you do don't buy a Hino cabover you might get in but getting back out will be a problem :laugh