Kevin,
Don't wish to disagree with you, and may others as well, re the crankshaft thread for flywheel and crank pulley, but they are not 5/8" 16 TPI UNS. They are of Whitworth form not Unified form. They are certainly 5/8" 16 TPI but they are a special non standard Whitworth thread.
The OZ worshop manual TP832 1971 has a section, A31 on page A20, re this thread.
BMC produced a special tool, 18GAO3 Crankshaft thread tap, "to rectify slight thread damage". See page s-2 special tools section of above manual.
The difference is in the thread included angle which is 55 deg for Whitworth thread and 60 deg for unified threads. For a highly stressed thread like this I'd want to make sure the thread form is correct. One of the first things apprentice fitters learned many years ago when different thread forms, but with the same TPIs, were much more likely to be encountered was under no circumstances to mix different thread forms. It's a recipe for disaster as the holding power of mismatched thread forms is a lot less than proper mating threads.
I think this is one of those bits of misinformation which has gained a life of its own over the years. The 5/8" 16 TPI UNS thread is a standard thread in the 16 TPI constant pitch thread series, similar to constant pitch threads such as Brass threads which are all 26 TPI, although I think these are Whitworth form not Unified form.
As they are a standard but uncommon thread, taps are more readily available than a BMC odd ball, one off, Whitworth thread.
I'll get off my soap box now.
Regards
RonR