As far as I know and have seen for the AD trucks the steering box is only on top of, not passing through, the frame.

If you plan to remove the pitman arm from the box most of the usual tool suppliers offer a special pitman arm puller that you may find handy. I've got a nice Snap-On version that works very well even on the stubborn ones.

I've only pulled a cab over the column..
But thinking about pulling the column from under the cab it may be handy to remove the left front wheel first to make access easier.

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
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-