Ok, here i am. I left him a PM already but i guess should leave a response here as well for any others that ever have this issue.
Basically that crack won't hurt a thing and can be left alone assuming the valve guide clearance is good. On BBC heads the guides are changeable and the intake is easy to change, the exhaust guide on the other hand goes through a water jacket and can sometimes be a pain to change a guide and not have water leak past the guide. I ALWAYS pressure test a BBC head that i've changed an exhaust guide on just for this reason. The exhaust guides are also different sizes along its length and MUST come out and go back in from the correct direction or you can crack the head. ALWAYS use a sealant on the exhaust guides when installing them but its not required on the intakes since those don't pass through a water jacket.
Like i explained in my PM to the OP if these heads came into my shop i would have tore them apart and cleaned and inspected them and then if the guide clearance was good i would then call the customer and let him know that the guides are cracked and that they could be left alone. I then let the customer decide what he/she wants to do. If moneys not an object then by all means replace the guides but if things are tight they can be left alone with no ill effects.
