Yes, I had considered just using the spindles on the old axle, and I have seen an AD COE done this way, disc brakes from the P30 but original I-beam.
I decided it is not as good of an idea as narrowing the new axle to fit.
At least for the AD axle the ends had to be welded on and beefed up to fit the spindle and king pin, not a very clean solution I thought, and somewhat questionable on strength at that point. the original axle looks about 1/2 the physical size of the P30, so not a lot of extra factor of safety on the modifications..
And as you also noticed, the Diamond T had issues with the king pin inclination angles of old and new not matching up, and now requires probably some serious bending to correct.
There is not much of a problem with steering as you thought, the I-beam it's self has no connection to the steering linkage, so if you use new spindles you use the new bell-cranks and steering linkage, at that point the old stuff it not an option any more.
So, yes I have considered it, I have seen it done, and I still like narrowing the whole thing.
Grigg
