Having worked in a Ford w/shop thru the sixties IIRC you will find even the UK fords converted or were UNC/UNF during the early sixties. The MKIV V6 engines used 1/2" bolts in heads & main caps and I think a service letter had some data advising the problems if we used any BSW stuff. The German car stuff was metric and IIRC the Ford Cortina ~ 1972 was the first UK body to use metrics, but the 1600cc x-flow pushrod remained UNC/UNF, but trans & diff were metric, along with the 2000 OHC pinto & 2.3 thru 2.8 German V6... however many of our old semi redundant BSW sockets now fitted most of the metric bolts.I Have just read this old post and I think Ryan has raised an interesting point. The cars built in England did they use UN or Whitworth fasteners?
Given that UNC and Whitworth effective thread diameter are so close makes them interchangeable other than 1/2". All engine and mechanical components made in USA would have been UNC or UNF at 60° and Whitworth 55°. I have seen Whitworth bolts come lose in UNC threads so How did they over come this in the day?
Bob, I have just superimposed that image over the bell housing bolt positions for the Windsor block. None of the bolt holes seem to line up.It's ugly, but here's a scan of the original MK2 bell housing top view.