id be careful with old jap windscreens, remember the autoglass guy telling me that my original EG screen wasnt laminated so would shatter a lot more ( or something along those lines ) and the new ones were much safer if something were to hit it. Could be why jap screens are lighter if it is true
Pilkington glass might be able to help as they do classic cars, i know they do bronze screens for the JDM EG's which arent easy to find