[flathead47]

Thanks for everyone's input & advice.
Tinkers links to some other threads were very helpful as well.
My takeaway from the three threads are , test the thread first with a good used bolt or stud to see how tight the thread is ,
if required clean the threads first using gun barrel brushes & cleaner ,
only chase the threads if they have been damaged by using a chase tap or a modified head bolt with 3 or 4 slots cut into it.
If the threads have been tapped using a normal tap it is not ideal, but thread sealers will prevent leakage & help with stud alignment.
The end result is to keep the threads as close to Ford spec as possible, so take your time & do not rush it.
Ian