What is a Euro Standard lamp?  When I was in Europe (albeit Germany)
they used the same headlamps as American with the exception of being
non-sealed beams as we required in the US at that time.  The only
country I knew of that used anything different, was France which used
Yellow headlights.  If you need to install something other than the
sealed beam lights that came on the car, you are either going to need to
find a conversion kit made for the car, or do significant surgery to the
light assembly to retrofit whatever it is that is required.  I know that
some american cars had an issue with not having yellow turn signals on
the rear, but the 88 would not have a problem with that.

hello, smekla,

in most of the european countries there are "HELLA"-Lamps used. HELLA is the
company. They are localized in Germany.

The respective HELLAs use H4 bulbs. They fit in the stock mounting. You can
find all the hardware for Your conversion at OPEL car dealers (with GM
offerings) or at the BOSCH services in Germany.