6 spoke are a little heavier duty I believe as you see them spec'd on vocational trucks such as trash trucks, dumps'wreckers etc. more often than Hyway trucks.
Tube type rims are flat across the inside of the rim. Tubeless have a raised portion in the mid part of the rim. HRL's size designations are correct.( as he did road service for a while and could proably tell many storys of mismatchs)
