You can thread as many D-rings as you want on standard 2" webbing.Honestly I dont like the looks of a 1 piece.....I like two d rings on each shoulder and more attachment points...I am running a metal detector ,lights , and pin pointer , plus a wreck bag to put the goodies in...I know exactly what I want in a harness just need to know how to make it... I bought a OMS comfort III and sent it back because it was to tight.. One guy said I could have added some webbing but for 800 bucks for a wing and plate I opted out of that.
Do you really need adjustment or just an easier way to get the harness on and off? If it's the latter, you can add a break with buckle on one side of the harness. Like this:
If you don't want to have to sew anything, you can create a loop of extra material instead of the break. Like this:
Both images are from this thread (link fixed): Subgravity Paragon harness