How much is your time worth to you?
I ask because your risers will give you headaches, your PSU(s) will give you headaches, your case will give you headaches...
It's probably just going to be worth it to spend $150 and buy a used board/cpu/ram combo and build yourself a new used rig. You'll be happier with it and you'll better understand what is going on with it when something breaks, it will.

That said:

Using 2 PSU's is fairly safe. I have run 2 in all my rigs in an always on setting, crossed the switch cables(green/black). I did this for about 8 months until I bought a pin removal tool and spliced the two together. I always worry about fire, not because of the PSU necessarily but because it's very hot, always on and it draws a ton of power.