Too little info, what kind of racing? Are you hoping to be competitive? If you are contemplating Huret, and you have presently a Seven, then this bike is relatively dated and not race competitive against peers on more newer equipment. Unless this is a C&V race, like L'Eroica with equipment constraints.
If this in an old race bike, it can be moderately updated to competently finish a race. But I'm not aware of a Suntour Seven ever being used for a race bike. It's a touring bike RD IIRC.
Pics of the bike would help.
But off the top of my head, I assume any modern Shimano derailleur will work fine. Available and reliable, slant parallelogram just like the old Suntours, 8 speed spacing range, index compatible. Of course, if this race requires period correct components, then search for another Suntour.
Last edited by WNG; 02-17-12 at 06:23 PM.