Sounds like you have a decent plan, but you do need to do the research as to what you need for the solid axle swap. This actually isnt as hard as it seems. I like to think about it piece by piece.
For instance you need:
A solid axle - obvious reasons why.
A way to hang the axle - Springs hang the axle.
A way to attach the axle to the springs - U bolt flip kit and/or stock U bolt systems attach the axle to the springs.
A way to attach the springs to the truck - For the front of the springs, the spring hanger attaches the springs to the truck. For the rear of the spring, the shackles attach the springs to the truck.
A place to put the shackles - They make jigs you put on your frame, and cut out a hole for the shackles to hang from
A way to steer the axle - Crossover steering is the best way to go about it.
A way to stop the truck - Landcruiser rotors and the stock IFS calipers work well.
Basically, just think about what you need, and what part makes it happen. Where you get it, if you make it, whatever comes later. You need to plan what you need before you can plan how or where to get it.
As for the engine, I think you might be a little too stressed out about it. I have a motor that was meticulously assembled, fully machined, etc and it tickes too. Ive checked valves hundreds of times, setting them hot, cold, different settings, replaced the adjuster screws, etc. Ive checked the valve cover hitting, whatever. Some motors just tick IMO. I think its due to the different materials they used for the rocker arms in different years. Now, if its KNOCKING, thats something completely different.
I personally wouldn't dump money for a rebuild into an engine that still runs. Like you said, you have your Mustang if this dies, so why waste all that money on a rebuild kit or a used motor or whatever, when all that could potentially just sit on a shelf in the garage for the next 4 years because this one keeps running? Of course, you wouldnt want to sell it all after you bought it because you'll keep thinking that the minute you sell it, the engine will die. I say screw it, drive it until it blows, whatever, THEN worry about it. If it blows, you have the Mustang while you collect parts ONCE YOU NEED THEM.
Thats just my opinion though. Is your schedule very full? I plan on heading down to my Dads house (down that way) sometime fairly soon (maybe today, maybe sometime this week). I could stop by and listen to it and give you my two cents on it too if you want. Send me a PM on when it might work for you, and I'll see what I can do if you want.
~T.J.