with 5lbs. of boost assuming the rest of your motor is stock im guessing you may be in the neighborhood 160/180 hp range...from what i can tell from other posts you should not have trouble with more boost, around 250 hp is certainly achievable on a stock block, although long durations at high RPMs is not recomended as that will likely cause block failure...and with increased boost i would also have to assume your head gasket would be the likely ''weak'' spot of failure if your head is still using the original head bolts instead of upgrading to using studs which will create a better clamping force,,,i would love to boost mine but i just dont think i can bring myself to do that to a restored original car,,, almost everythin im doing will be un noticeable as to retain a OEM apperance :)