I posted a month ago about an end play problem with my 440. I tore it down yesterday the block looks OK so far. I still need to tear it down the rest of the way and see if the debris left scratches and such.
Here's a pic showing the thrust bearing and the grove cut into the crank:

Can you see any protrusion that was cutting that groove

I feel your pain. I just went thru 2 small blocks 318 and 360 that did the same in my 84 d150. The only reason I could come up with as to a cause is the torque converter "balloning" when I was pulling a load. I was able to find a replacement crank cheap in both cases.I did talk to a crank grinding place about it and they said that the cranks could be welded and resurfaced so if yours is a steel crank it may be a way to recover it.

A problem I have read about on another site was the crank thrust surface finish was not smooth enough causing excessive ware. I dont think many machinist really look at that surface at all when they polish/refinish a crank. This a a prob with many 5.0 ford racers from what I have read. They resolved the prob by using a much finer polished finish on the thrust surface. Is it a 4sp or auto?? Another 440 locally here had the same problem after a few hundred miles. Let us know what your machinist says.

I don't remember your former post, how much end play, in thousands, do you have now? Was it checked before running the motor and if so how much was it originally? Last question, do you know now why it became a problem? If not find and correct that problem before running the motor after you fix it

I can't say what the end play was after it was built, but 3/16" was where it ended up. In the picture you can see a groove in the crank thrust face that should not be there. The bearing has metal galled up on the inside radius and the surface is way gone.
I have another crank. The machinist said to bring it over with the other parts of the rotating assembly for a balance job. Also said the block would need cleaning to get the bearing material out.
While I’m at it, I’m going to swap out the automatic trans and put in a 4sp.

My computer took a dump over the holidays so I'm a little slow getting back sometimes.

You picture is blurry , what crank is that ?

It's a cast 440 crank. Here's a better pic of the crank wear. The groove should be a flat surface.

link no worky

And another:

first thing I see is you have a wide thrust crank and a narrow thrust main , the more surface area on the main the better .

Now what caused that , is that on the front or the rear of the bearing thrust ?

I don't remember your application , 4 speed or auto ? Race ?? Nitrous ??

A cast crank should definitely have the wide flange thrust bearing to reduce the wear on the crank. The '74 and later blocks used the larger thrust bearing, but it looks like you have the smaller bearing in your engine. It's VERY important that the thrust bearing main cap is aligned/set during assembly, too. Make sure you're good as far as a pilot bushing if you're going to put a 4 speed behind a cast crank.

Narrow flange bearing ate the wide flange crank! Now I've learned something new. Thanks!
I wonder what the chances of this happening with the correct thrust bearing installed?
The damage is on the rear thrust side. It was connected to an auto trans. The motor has 1,000 miles or less. I've never had it on the track, but I do like to accelerate at WOT when I have the space. The only questionable incident I can think of is when I hit a small patch of mud and lost traction.
The replacement crank is steel.

Besides what the guys are saying about the wide vs narrow
bearing I swear that in the first pic the left side
has way more wear than the right side BUT that may be
the pic or angle of the pic

When you are putting it back together [with the wider bearing] file a chamfer on the parting line of one of the bearing shells to pressure feed oil from the bearing oil groove to the thrust surface, every little bit helps.