Uhm welcome to the forums, search seriously just use the search button and you'll get a lot of info there right from the get go.
Next item of business and while I realize you can't be bothered to search on a forum I don't know why I bother suggesting this but....search the junkyard for the light to fit in the sidemarker. I believe as a temporary fix I modified my sidemarker light so that it would fit in the socket to last me a week or two. I went to the junkyard & took my light in with me (I made sure that it was ok with the "front desk" of the junkyard) and I just started taking bulbs off of all the nissans I could find, and wouldn't you know it I found some exact matches. I can't remember the car model anymore it might have been an S12, I just remember it had a honeycomb front grill and it might even had popups but I can't be certain (stanza?) anyway they're out there you just have to find them (coincidentally it's like information on zilvia it's on here you just have to do the legwork to find it)
As for your bumper support issue, you have two options 1. acquire a 240sx bumper support and cut it down to accomodate the silvia front end 2. buy a silvia bumper support.
Good luck and remember to search ffs
