I guess I'm the new guy

I've used K&W Permanent Metallic Block Seal Head Gasket Repair (http://www.uniquetruck.com/p-28744-permanent-metallic-block-seal-head-gasket-repair-16-oz-can-12case.aspx?affiliateID=10056&gclid=CJiSxLXe4tMCFQwQgQodvnwNmA). Requires draining and flushing the cooling system before putting it in, and after. Won't work with anti-freeze in the system. It works pretty darned good! Thought my daughter's car (Daewoo... 7-8 years ago...) had a cracked head, so tried this because it was hard to find a used head. Sealed it up, and ran for 10-12 months before it started leaking again. Found a head in a salvage yard, but pulled the old one first. Turns out it was a deteriorated head gasket, not a cracked head! This had sealed it until it deteriorated further. I'm pretty sure it will seal any cracks, at least until/unless they get bigger after sealing. That's always a possibility, but just keep the cooling system up and don't run it hot (boiling over hot) any more and it should last a long time.

If I knew the head was cracked I'd use this before Bar's leak, though Bar's Leak is good for cooling system leaks. I'd replace the head gasket though, not that hard or expensive, and have the head trued as well. It won't seal good if not flat. I'd have pulled the head on my daughter's car if I had suspected the head gasket instead of using a sealer product. 

Use an electronic voltage regulator:
http://www.worldpowersystems.com/AMC/dashreg/index.html
Just need a 5V regulator and some soldering skills...

I bet you're thinking about the generator or alternator voltage regulator. The voltage regulator for the fuel and temp gauges is separate and on the back of the dash. It is a small "can" type piece, similar to a rectangular flasher. Google "LM7805" and you will get a pic of the electronic regulator. The mounting tab is also a ground, or you can solder a wire to the middle leg of the regulator (or the tab if you can't find a grounded screw on the instrument panel). I would ground to the panel somewhere, not just to the car body, though that should work. One of the traces from a light bulb should be ground.

All Tom did was run a small short screw into the pin holes where the regulator pushed in. One is 12V in, the other 5V out. He bent the legs of the regulator up over the regulator body and covered with epoxy after soldering the wires on, and since he used the mounting tab for ground cut the middle leg off. The epoxy is not really necessary, I've been running mine without it since 2003.

The old regulator is very much like a flasher. It has a bimetal strip that cuts on and off with heat. Hook the output to a digital voltmeter and you will never get a steady reading. An old analog (needle) voltmeter will bounce between 12V and 0V. The gauges don't need a steady 5V -- they work just fine with an average voltage of 5V. The regulator switches 12V on and off quickly, so the average output is 5V. But it bounces up an down a lot! Eventually (over MANY years... 20-40... some originals are still working!) the bimetal strip wears out and breaks.

The gauges are just as happy with a constant 5V as an average though. There is no difference in readings with the electronic constant 5V regulator than with the old bimetal averaging regulator.

On a new (old) car to me I usually pull out the speedo cable and lube it with a light grease. It may not be the correct way, I don't know if there is anything in the TSM about it. The grease method has worked for me.

If it is the speedo unit itself that has problems then I would take it to a speedometer shop for repair.

Would be easier for you to try and score a different dash panel that has nothing wrong with either of those two items?