I've just completed completely rebuilding a corsa 1.2 (Z12xep) main & big ends,rings,head work,valve stem seals,tappets etc, (spent £400+ on parts )
getting the valves out is easy compared to trying to re-fit
the collets are tiny ,there is no room to get in to put the collets in place,
then PING ,spend half hour looking for the 2 collet sections that just fired out to who knows where.
i put the head on an mdf board with a cloth to stop the valves pushing down ,
pushed down/compressed the spring with a tube with 2 prongs fashioned with an angle grinder spring end, cloth pad the other (pushed tube with my chest ,stuck the collets to my fingers with grease to get them in place )
was a total nightmare , i have a big valve spring compressor and a small pickavant one, neither worked.
ok, so i have fat sausage fingers ,
took me all day and evening to get 16 valves (which i had lapped previously ) back in .
someone on ebay sells 2 collets for about £6 when you loose some
i suspect your local engine place has special tools to put the collets back and can do the job in seconds for peanuts
I would not do the valve re-assembly again without finding out how much it costs to be "someone else's problem"