dunno about s62 valve length... know only that they are 35mm/6mm 
I would bet they are the same as the M62 or shorter. bmwparts.info lists the valves as 48 grams, 2 grams lighter than the M62 valves.
Just looked it up, BMW S54B32 (E46 M3) intake valves also have a 35 mm seat and 6 mm stem. They are listed at 51 grams so they might be longer, enabling cutting to length and what not to make them fit.
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And another possible selection (though expensive and high quality) is Ferrea valves. They have blank valves you can purchase in either titanium or a steel alloy. Also since the valves are blank, it would avoid any problems with sizing and fitment. But they do cost a lot, $20-$40 per steel valve and $100+ per titanium valve. Hehe, 16 titanium valves would be around $2000
Part# / Type / Head Dia. / Stem Dia. / Length / Tip Length / References
Titanium:

Competition Plus (steel alloy?):

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People with the pre-9/92 M42's already are switching from 7 mm stems to 6 mm, so
why not go a step further and go to 5 mm stems? This switch would save a lot of weight if it worked/was possible.