what kinda headlight are you wanting to install?
if you are wanting to retain the stock light there are a couple ways to go about it.
1... permanent install... use a 3m or sem 2part epoxy/glue (found at any autobody supply store) make sure to get something for bonding the acrylic h/l to the fiberglass. cut a hole prep the surfaces... glue away.
2... almost permanent... but the headlight is removable, find a section of a stock upper.... basically about an inch around the headlight mounts and including the headlight hole... use the same kinda glue... but for bonding the plastic to fiberglass. prep the surfaces... glue it in.... then cut the hole out using the inside piece that you glued in as a guide.
the problems are obvious with the first option..... if you crash... and break the light.... you be screwed... cuz the glue is good stuff.... and you will spend hours trying to get it ready for a replacment light. the second makes light changes as easy as the factory intended.... but the headlight will be recessed the thickness of the fiberglass... not really a big deal.... but not really all that attractive either.
now if you want to install a projection beam style light... that can be done also.... just need a lil fiberglass know how.... as you would have to build something for the light to mount in.... then fiberglass it to the upper... then still figure out how to install the light in it.
if this is something you dont feel comfortable attempting... shoot me an im... startin to hit my dead time of year... and can always use grocery money