67 Cutlass Freak

Let's say you just purchased a new set of heads... Ebrocks, Pro Comps, or worked over cast iron heads. What types of problems did you have? What were the common issues? What type of information did the supplier not give you? What did you have to call their tech line about? I'm just trying to learn here, not trying to cause a **** storm.
Thanks in advance, Dave - The Freak