Someone, I wish _I remembered who, posted up a pdf version of some rather good modern rules a couple of months ago. I read it and it seemed like good work.
Links or it didn't happen.Gamma World provides a solid core system. You'd just need to strip out the mutations and create some classes. Hell, for the LOST game I'm running, I basically made a 4e Modern ruleset that fit on 4 pages.
links or it didn't happen.
but seriously, you've always produced top notch stuff for non-traditional d&d settings (renaissance and up); let's see what you have!