Mmm, i only brought them because they seemed highly recommended for putting the head on nice and tight, theres so many opinions flying around though..
Ford standard head bolts are proven to over 300bhp, the con rod bolts are not.
Ford use stretch bolts for several reasons, as far as i know the main reason is to accommodate the different rate of expansion of iron and aluminium when heated.... your block is cast iron and your head is ali.
Non stretch bolts, not only need the all important re-tighten after a thermal cycle, but will not allow for this differential expansion.
Ie, send em back and get some more money to build a decent engine, have a look at my project page for tips (haven't updated it in a while though!).
Good luck
Rob,