Oy pingtang,
I just finished a McLaren MP4/8 and, like you, I painted the red instead of using the decals, using an airbrush. I had a heck of a time getting the color right. I couldn't find a Tamiya flourescent red in the jars that was even close, so I first tried Testors Model Master acrylic flourescent red, #4703. It looked a bit off color, but like an idiot I masked the model and sprayed it on anyway. Awful!! Way too orange. After stripping the whole thing, I primed it again, sprayed the white again, and then used Testors Model Master enamel, #2041 (28913) flourescent red-orange, with just a drop of Testors Model Master enamel insignia red #705 (31136), at about 20:1. This came out really well, and it matched the decal colors perfectly.
If you're set on using a rattle-can instead of airbrushing, I'd suggest you try the canned color on some scrap first to test color compatibility. One would hope the Tamiya flourescent red would match their decal color, but don't take chances...
Good luck with it, and let us know how it works out.
Glenn