The original bearings were Ø1/2 x Ø1-7/16 x 11/16 inch. Those have been obsolete for a very long time. When old stock does turn up on the market, the cone itself often goes for over $200! SKF W5700 and Timken 00080x cone and 00152 cup are part numbers seen.
I have heard of the substitution of Timken 00050-00152x, which is Ø1/2 x Ø1-7/16 x 17/32, which is currently in the Timken catalog. However, a few things to keep in mind. First, it has a shorter hub, so spacers would be needed under the bearing nuts, or longer bearing nuts made to suit. The second difference is the cone sticks through the cup by 0.022 inch, whereas the original had the face of the cup and cone flush. The third difference is the new bearing does not have a generous radius on the bore of the cone at the ‘small’ or inboard end. They have the big radius at the other end, expecting a diagonal load path across the bearing and races. They don’t seem to have envisioned a situation the way Kingswood uses the bearing, nipped up hard against a shoulder on the axle on the one side. Not anything that can easily be done about that, it just means a regrettably sharper radii on the axle, and a higher stress concentration. The usual way around this is to make a false shoulder on the axle with a spacer or a groove behind the shoulder to redirect the stress path. Alternatly you can grind or turn (with a CBN tipped tool) a larger internal radius on the bearing race, depending on how keen you are. A potential fourth issue is the cage of the Timken 00050 cones might foul the sheet metal cup (#8325-1) that keeps the felt out of the bearing. This based on the 3D model that Timken provides; I do not know if the real bearings have such a long cage. The cage could be trimmed or cups with more offset made.
'Fat axle' conversion:
The bearing is pulled up tight against the shoulder on the brake drum side, so some dimensional correction will need to be made in light of the several above differences to retain the correct alignment between the brake drum and the backing plate. On the other end the bearing floats and is where you set the bearing clearance, so things are not so critical.
However you are still stuck with a Ø1/2 axle. The originals were made of a 5% nickel alloy steel. Even so, as you found they are typical bent and that quickly ruins the (expensive) taper roller bearings. Source of NOS axles, are you joking? The first improvement would be to make the center portion larger than the original Ø9/16 forged diameter. Still, it has to be reduced to a Ø1/2 where it passes through the axle and it is a long way to the frame lugs. Nor does it provide a shoulder for the bearing to seat against. It sort of nips up and sticks on the radius.
Original axle layout (cage and rollers not shown):
If making new axles you might as well convert to Ø17 x Ø35mm x 10mm sealed ball bearings. You can use the original hubs by making a sleeve for the outer diameter, split to ease installation (and removal!) This allows for a significantly larger diameter through the bearing and the bearing nut for a stiffer axle. Outboard of that it can be reduced to Ø1/2 so the frame and forks need not be altered. If it bends a little out there, it will not harm the bearings. When using original hubs (vs. making new) you will need to take a shoulder to shoulder measurement between the bearings of the hubs as I am sure they vary. With the ball bearing design there is no adjustment, the clearance is machined into the corresponding shoulder distance of the axles. Of course you can skim a little more off or add shims if the machining is a little off. While the link below is an article primarily aimed at replacement axles for the 1936-38 Aero, the same idea would apply to the S5/S6/T6 family. So use the axial dimensions from you original axles. For example on the S5/S6/T6, #9384 (rear axle) is 7-15/16 inch overall and #9382 (front axle) is 8-9/32. The bearing nuts are Americanized threads to suit my conditions, but they could just as well be metric.
https://www.douglasmotorcycles.net/aa-files/documents/2010/heavy-duty-axles.pdf-Doug
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