do you really need a special windshield for the HUD display? while i am a newbie to the Bonneville, i did add HUD to my Cutlass (with non-HUD windshield) and the display is crystal clear. as a side note, i did get my windshield replaced before i added the HUD. they asked me if i had HUD and i told them no, but the HUD works great with this windshield.
It helps to reflect the image better during the day... they also sell a film that you can put over the part that refects the image better. Granted you can see HUD with a regular windshield... it is reccomended to use the special one.