Why do we keep throwing rods? (Page 2 of 6)

That's looking like a pretty good theory.

You have oiling issues.
Look at the big- and small-ends of these rods. There is oil coking at each end.
Also, if you look at the bearings, ALL of the tin has been wiped off of the face of the bearing.
At most, you should only see a little copper showing at the center of the face, basically from about 5 o'clock to 7 o'clock and possibly 11 to 1 o'clock with the small end at 12 o'clock. (Too many clocks.) That is usually caused by cold starts and low oil pressure when it does show-up.

Those rod bearings are completely free of the bearing material. The copper is designed to provide a softer surface that the steel backing if you wear through the bearing tin. Also, the copper helps provide a place for metal debris that would scratch the crank journal a place to go.

If you look at the piston pin, there is coking around the pin, but not on the skirts. There is some on the crown from combustion heat, but that's where it stops.

My guess is that you cross-drill the crank throws, and then chamfer the feed holes.
You may also need an oil restrictor to the upper portions of the engine.

What do the main bearings look like? That will help diagnose if the oiling issue is before the crank or just at the rods.
Go talk to a race engine builder with those parts in hand, or a lot of pics.

Actually, DelinquentRacer brings up a good point. The engine in my car has a restrictor in the oil feed to the head. If you lose that too much oil goes to the head and not enough to the rods/crank. Worth a check to see if you have one or if it's missing.

All of this pictures show either piston, rod or rod bolt failure.
Oiling did not cause any of that damage.

safety wire the rod bolts?

Its difficult to say, a nut will back off after a bearing spins when everything starts hammering/galling.

Did you measure the length of the rod bolts before and after they were torqued? If you measure the loose survivors are they longer than their torqued length?

If the engine had detonation you'd most likely see detonation "waves" in the carbon on top of the piston. I'd also go with revving too high as the cause. It will start stretching the rod material. Also when installing rod bolts burrs can hold up the bolt from seating properly and get pounded into place. I'd guess this isn't the root of the problem though here.

My guess is the bearings are not lubed as well as ideal and it's being revved too much. Honda's are super blow uppity because their stock "street" rev limit is too high for race use. Just because "they" or the "experts" do something and use it as a rule of thumb doesn't mean it is right and or will be fine under race duty.

This isn't very scientific, but we have seen that some engines (e.g., Honda B, Chevy small-block, Toyota R) just love to throw rods in Lemons racing, and no magical cure (other than draconian redline enforcement) has been found for them. We  haven't seen many Ford Thriftpower 144/170/200/250 engines in Lemons (actually, the Billy Beer car is the only one that comes to mind, although I'm sure I'm missing at least one other), and knowledge gained from the drag-racing/street world isn't going to be very relevant for Lemons race conditions. Maybe it's time to try a torque-demon 300 and set the rev limiter at 2800!

I s'pose by posting I am essentially saying that the failure is caused by oiling problems.
Overheating the rod can cause a multitude of issues.
I've never seen a rod nut back-off on destroyed engine bits, either.
There is not enough info to come to a specific, diagnosis. Also, there are too many cooks in the kitchen.
One nice thing about over-budget engine builders is that they assemble the engines the same each time with, usually, proven techniques.

So, from the oil coking on the rod ends and the bearings that have NO tin/babbit layer, that engine has oiling issues. Those rods are seeing excessive heat.
Pull the bearing shells and the steel backs will be severely discolored from heat. That heat is only developed through excessive friction.
Not enough oil flow or not enough oil wedge/film (tight clearances).
Pics of the mains would help.

1) Use a good synthetic oil.
2) Make sure that the rods are round. Use the good bolts without washers and add blue locktite. Get the right torque value. 5/16 is about 38# normally .
Shift it at  5500 or less.
That 20-50  dino  oil is most of your problem.  No real race engines run dino oil.   Add annoil accumulator of some sort.  Mine cost less than 50$
Pics here,  http://gallery.oracool.net/v/album82/protech/Cheaps/

Pretty sure a Ford 200 six isn't considered a "real race engine"...    We ran 20/50 dino oil in our gas motors for a couple races with no issues caused by the oil.

Thankfully, the experience was through durability testing engines at work and not personal experience. 

"Dino" oil [synthetics and conventional oils are both made from fossil fuels, it is just the purity of the base stock that changes] is just as good at providing protection as synthetics, EXCEPT under extreme circumstances.  That being said, the extra margin that it provides in our environment is probably worth it.  Normal running engine won't care, but if something goes wrong, it can provide enough extra protection to get an extra few laps.  The propensity of synthetic oil to increase leaks is partly an old wives tale.  They can have more detergents that will dissolve deposits and lead to possible leakage.  However, good conventional oils can do the same thing.

Loose rod bolts/nuts will lead to bearing failure.  The bearing failure then leads to the locally overheated oil, which can cause the oil coking seen here.

Again, to properly diagnose this, we need to see the other bearings in the system.