heres the guy whos making brackets...
https://www.facebook.com/RRFabs/
so $100 for Silverado headlights and another $200 for the brackets. sounds like a steal to me versus $500-$1200 for Silvia headlights, most of which are beat to shit.
oh and dont forget that the Silverado headlights are actually aimed for LHD roads, unlike S13 Silvia headlights which are set up for RHD roads.