pre 69 or later axle for my application? wheels..

[dmartin1]

What do you guys think is the best bet for me at the moment on the rear axle.

1969 shortbed fleetside, its got the narrow rear axle.
4/6 ece lowering kit.
This truck will eventually be going on airride suspension.
I plan on going woth 20" wheels.

What i really need to know is shoud i retain the narrower axle? Am i wrong to think this is better as it will allow more wiggle room for backspacing?

Or is there an advantage to the later and wider 5 lug axles as far as wheels and spacing goes?

cost and parts aside, just confused on what is going to be better for my application.getting a headache over this

any advice is greatly appreciated