I am not sure I completely understand your reasoning and measuring/figuring.
But I trust you have your head wrapped around it better than I do.

Two things to consider:
1. Make sure the brakes and steering linkage fit in the wheels you want with the back spacing and adapter combo you have planned.
2. The ideal place for the center of the tire is directly below the centerline of the king pin, or in your case, below a line drawn through the center of the ball joints/king pins. this allows for very little tire scrub when turning, and easy turning. If it is very far off it may handle funny on the road, not sure?

I guess what I am trying to say is I don't see how you can use a dual wheel or a single wheel on the opposite kind of front hub, because of brake clearance and turning geometry, even if you do use a small spacer??

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-