Glad that you bring up these questions and or concerns.
From the sheer size of this thread it shows that we all have been having a lot of fun and it all looks good a dandy, but safety comes first and foremost.
As you'll know, I came on here as a guest and for the reason of Mopar family, I felt it to let out all my suggestions, tricks and mistakes in full transparency. But, let me assure you that I value all the input from everyone and I also value my safety and the safety of others because as we all know in drag racing, everything is about hurry up and wait to only go faster. but Murphy's Law happens much faster and I would only want to make and play things safe.

To answer in the order of presume.
*The light weight K members made out of thin gauge stainless PROBABLY failed because of the extreme stress from lifting and then crashing down forces incurred during a wheel stand.

After their debut to dominate the fields with their altered wheelbase weight advantages and with victory wins almost from the start, all those AFX cars of yore were known to carry the wheels a good distance while being a wild ride all the way down the track. It was a audience sensation and shortly after were encouraged by some outlaw tracks to do such wheel stands for entertainment purposes until it became inherently dangerous. As a result, a memo was sent out by the factory to all the factory drivers to stop all wheel stands immediately.

In fact some teams were warned that their respective contracts would be revoked if they continued the violent wheel stands in fear of crashes and product looks. Someone forgot to give such memo to Dick Landy. LOL.

In contrary, today NHRA presumably wants their future Pro-stock cars to have items removed or installed that enable them to perform some type of limited wheel stands at launch. Who knows how that rule will limit itself in the heat of competition.

*I've got rifle drilled aluminum hood pins on all four corners, but with an adjusting tube center for strength and adjustability.

*An Aluminum exhaust is only holding up its own weight which in this case is almost nothing. It is beyond the fail temp once at the collectors and rearward and Yes, it will temp loss at heat cycles but a strict multi-point inspection of the system for cracks or looseness keeps me worry free. I have a few Aluminum hangers through out the system to keep any cracked portions from falling off the car in motion.
I had thought about corrosive gasses when first entering the idea of an aluminum exhaust, but the issue of corrosive gases at different temps is a mystery to me in all honesty. Steel, stainless or iron go through the same phases. Aluminized steel tubing itself seems to have survived many years of on/off usage from what I've seen.

One thing you bring up that I was seriously thinking about was indeed heat loss. True that heat loss can effect HP, but I took a gamble at weight loss over the heat only because I used to run open pipes back when and now run an exhaust system that is relatively short dumping at the rear differential without tailpipes and believe that it has little to no effect on the flow.

Many cars out there, be it factory or custom or race run with aluminum hubs, drums and calibers where different temps of heat and cold are constantly introduced on crucial suspension parts.

No new ET numbers yet, but I can safely say that my car feels a lot more reactive now with less weight, less heat in the system than ever before. It could honestly also be Thumper's magic on my carb as well.
I'm just looking at all the suspects of change that have been performed lately. Maybe too many at the same time.

*As far as the trans cross member, the reason I've painted it gloss white is to have good looks at it during under car inspections. (A good habit)
I've only heard of a couple of failures with the factory cross members made out of steel and for the most part seem to be a result of miss-aligned transmissions/drivelines, bad vibration issues and or bad factory designs from the very start. Some cross members have extreme load bearing mounts that were ill-designed or ill-welded in the first place. Has anyone ever taken a good look at factory member welds? A good case is the factory steering box welds to the K member. I've heard of some of those breaking loose.
I reinforced my steering box welds because of concerns with a manual steering car which applies more stress on the tires and suspension more than a power steering unit in motion.
I've never broken my steel trans cross member that I had before partly because I also had the trans mounting bosses closer to the members center where it is more stronger because of my engine setback. (Long standing secret).

*Titanium in the right T type is stronger and less stressed then steel because of more shear and tensile strength.
F1 cars put Ti bolts to the test equivalent to many miles on a street car, especially a lightweight street car.
Though, honestly, those types of cars have strict maintenance programs in place. I do as well.

*No composite leafs on mine, though I know of some out there. Hee,hee.

*Lightened Dana rear on my car with a few unique tricks but not much weight shaved. (No I ended up not going for that supposed new wave all aluminum Dana 60 rear. They were a little stiff in answering my longevity strength questions.)

*Factory A-990 seat mounts have been flawless in my car for years, more than 15 years now and on many other Race cars that see more stress than my street car ever will. In fact I probably bought the first sets off Kramer Automotive back in the 90's.
I've also installed large washers on the floor mounting bolts to spread the load of my body shift weight during launches and quick stops.

*I have not reached the Leaf front hanger bolts as of yet. Though I have thought about them.

*I've looked into Titanium U bolts, but no one wants to machine/bend them for me with the correct flat spot on the top for more grip on the rear tubes. I do have a set of 8 Titanium long bolts on future order for the existing steel U-bolts though.

*Carbon Fiber is too easy and expensive for such a piece that can be easily nicked and shredded in a street environment.
Dynotech made me their very last metal matrix shaft just before deleting the material from their line up. In fact, my order hogged up the last length of matrix tubing that they had.

My handle of FULLMETALJACKET is for just that, the car is a full metal jacketed project. Made of many metals. No fibers or plastics of any kind for opaque items.

I'm not sure what TB's mean?

*I've run my rear drums without the parking brake mech for years.
Again, this is almost like the Woodward garage test mule back in 68' but with a concern for safety.
I for one do not encourage such crazy things unless they were thoroughly engineered, planned and or tested by logical persons.
I'm just showing what could be possible.