Jay,
Along with all the others here; hearty congratulations on an inspiring victory.

Yes 280 sounds like the number.
And yes they all break at the seal groove.
Yeah it kinda drove me nuts for 2 weeks. I questioned everything I was doing after a lifetime of no probs.
But it really seems to me it's a manu/metal problem. And I'm not a basher just a realist.
BTW just measured the width and it was a chore to press the caliper to 3.22.
1310s should measure 3.219. I know that's close. I only mention it because the Mexican joints were a tight fit in the yoke. The old American joint fell right in.

IMHO. Nailed It!
From what I know about U-Joints..  the fact that the Mexican part (the one that failed early) is a larger O.D. than the American part (the one that's still alive) would likely cause very high pressure on the needle bearings (as others have suggested) in each of the bearings caps that are a tight fit whenever said tight cap rotates through the 'pinch point' since U-joints aren't constant velocity the bearing clearances have to be right. Next up, as you say, would be addressing the operating angles which your traction bars have been partially doing.
Interesting info about the MOOG/Federal Mogul two tier quality issue, coincides with an input from a trusted auto mech/racer who has also informed me that there are two quality levels available from MOOG. From what I was told one has to be very specific in the request for "MOOG American Made" in order to get the good stuff, and the price is commensurately higher.

Below are some links for SCE's current shim steel and composite head gasket offerings for the FE. As I mentioned before, the 4.400" bore will be in the same style as the last of the gaskets below (p/n 534254).

http://scegaskets.com/product/sce-gaskets-part-number-534252/
http://scegaskets.com/product/sce-gaskets-part-number-534402/
http://scegaskets.com/product/sce-gaskets-part-number-534304y/
http://scegaskets.com/product/sce-gaskets-part-number-534174/
http://scegaskets.com/product/performance-composite-head-gaskets-for-ford-fe/

"Wouldn't I want a head gasket to fit the bore of my block ?"
As Jay said, practicality is a driver as tooling can be very expensive. However, many times while assembling the engine, cylinder head interface with the gasket is forgotten, simply because it's never in view. The head gasket manufacturer must take into consideration the shape & size of the combustion chamber as well as the bore opening in order to offer the best transition from cylinder bore to combustion chamber.
Often times the bore is much smaller than the combustion chamber especially at valve locations that have been un-shrouded. In this case a head gasket with a larger bore opening than the block is required or failure is imminent at the point where the fire-ring is not in contact with the head (usually near a valve).
In the reverse, where the edge of the combustion chamber is inside or very close to the bore opening, the head gasket would, ideally match the bore opening.
What you really want to avoid is a head gasket that is significantly larger than both the bore opening and the chamber. This creates a void or gap around the entire bore, adding wasted cc's to your swept volume and increasing the probability of pre-ignition.

Suggestion: before settling on a head gasket choice, flip the heads over and place a sample of the head gasket on your cylinder head in the installed position. This will give a you visual and perhaps save some frustration in the future.