the mount needs to be farther out so that the center of the tire is where it is supposed to be so that the suspension geometry is correct. i do not think that putting single wheel hubs on it will gain you anything in trying to make the track narrower.
If I'm following along so far you've picked up a 5/10 lug P30 chassis and it has dual wheels, which is good.
There are no single wheel hubs to swap. You couldn't/shouldn't run deep dished dual type wheels on single wheel front hubs anyhow as mentioned above it messes with the steering.
To come up with a front suspension narrower than what it is already you need to do some cutting and welding.
What widths are you dealing with old and new???
Grigg
