i ran 20psi on a stock block for about a year. it never blew. i just wasn't going to wait for it to.
with stock injectors, 14psi no more.
with 50lbs and turbo/maf upgrade, 19psi or so.
72lbs and turbo/maf upgrade, 22psi or so is the most i would do stock block. but you are playing with fire with the headgasket and ring lands.
Shaun