Exhaust valve face angle 45 vs 43 degrees

I'm sure they don't. That being said - that spec is for a single angle valve job for use with leaded fuel that helped protect and lubricate that exhaust seat. About 8 years after that was published as a spec performance valve jobs were on hardened seats, with multiple angles, for use without the lead. There is no performance or longevity reason to use it now, and a shop would have to buy and maintain another specialized cutter for it.