hey Zeuce,
imho if it was my bumper, i would get it professionally done or buy used bumper off the forum. there should be a few 40th owners that are willing to part with their parts if they already aftermarket kits. With that being said, i still think this is a "do-able" project.
i also own a 40th Z and i found that finding the correct paint match for our cars are nearly impossible. Ive had some good luck with automotivetouchup.com with spray can paint. I know other members that've gone through this website has had bad and good experiences with their paint. I was one of the lucky ones. I painted my carbon signal TS style lip (FRP material) with great results. I want to say my paint job was 8/10 and my body work (bondo, sanding, primer) was a 7/10. Here's a link of my project...
DIY- Painting front lip progress!
My advice is to concentrate more on the body work than the paint, Im not saying that paint is not important but any imperfections with body work WILL come through the paint. As for painting the bumper, it may difficult to blend the paint with "spray can." I say this because, painting with spray can does not give you a constant spray pressure as a spray gun would. Making sure your spray tip is always clear and not clogged.
Another thing to keep in mind, when placing down your clear coat, is to use a 2K clear. It has a two part hardener and seal which will give your paint job and heavier coat. This stuff is super toxic for your lungs so i suggest you use the recommended protective gear.
I know others can chime in, about this, good luck