HI All,
The big difference between Ford and BSA is that the BSA is aircooled !!!!!!!
I have seen a dropped valve caused by the liner dissapearing down the exhaust
There are a couple of ways of removing the guides that do less harm to the heads
1) drill and machine away the guide above the head face and push down the guides into the port
this means that any carbon/crap does not get dragged iin between guide and head
2) drill out the guide as much as possible to weaken its grip on the head
3 ) tap a thread in the top part of the guide and then use a punch against a stud threaded into the top of the guide, this way the guide tends to stretch and shrink rather than compress /fatten
4 ) if the guide top is machined away then tap the bottom end and drive downwards or combinations of the above
Always heat the head to 200-220 deg C before removing or replacing guides
HTH
John