Old bikes are the art of the possible,unless you happen to be a billionaire,and can afford to replace any part with standard,when you find bodging.
That is of course true, and I do like creative bodges (as opposed to botches). However, going back to the original point, Imperial threads cost little more than metric so why not use them?
I do have to confess that on my last modern bike I extended the gear lever and used 5/16" CEI to attach the new toepiece.......