I would go PBM HMIC and do this conversion:
180sx with Silvia hood

Cheaper than any Silvia conversion and functional. With the PBM HMIC, you'll lose 30lbs up front because you have to ditch A/C. The pop-ups weigh something like 13 lbs each.
Throw in a carbon fiber or fiber glass hood & you're looking at getting rid of over 80 lbs from the nose end of your car. Even more if you relocate the battery to the back and/or are going from KA to SR...