You want to learn to custom water cool on old equipment?
Are you willing to accept the cost of it will probably exceed the price on your entire hardware by not a little, but probably by double?
Sure you can reuse some of the gear, but some you can't like tubing and the gpu block.
Is it risky?
Yea its always risky playing with water near live electrical components, but the results are amazing if you do it right, and don't cheap out on the budget.
Been water cooling for more then 14 yrs now, and i probably have lost more stuff to count from stupid things which resulted in leaking, but at the same time i am probably more knowledgable about it then Linus and Jay2Centz are, as i have learned from the watercooling founders (Cathar + Marci) directly.