Hood spoilers are really not that difficult to install if you are experienced with drilling - the factory celica hood already has all of the drill locations noted on the under skeleton.
Open your hood, look at the underside of your hood for the only holes in the skeleton that look like they are there for no reason (ie, holes without bolts)... These locations are where the holes for your bolts should be drilled.
ALWAYS DOUBLE-CHECK ANY LOCATION BEFORE DRILLING ESPECIALLY IF YOU ARE INSTALLING TRD REPLICA HOOD SPOILERS
As with MOST bodykit pieces, this should be installed by a professional - but I've posted these photos for anyone who is curious as to how/where the actual install points are located - these photos should answer most of your questions