Here are a couple of places, though neither is perfect:

http://cycloawaodorin.sakura.ne.jp/FZGX/customize.html - KAZOON's website. This only gives you the part names, machine names, and machine weights. But it's easy to use otherwise.

http://backup.segakore.fr/f-zero.jp/f-zero_gx/customize/index.html - Backup of the old official GX website. This actually visualizes the machine and shows the grades of each part, but the part and machine names are in Japanese.

This site has english part names, visualizations and even that radar diagrams for body/cornering/acceleration/max speed:

gsv.xii.jp/fzgx/

It is the only place I know that computes those radar diagrams - it uses javascript, so the equation for them is probably hidden somewhere in the code. Unfortunately, code comments are in japanese.