Will a torque arm that fits a 1990 camaro fit my 98?

 

Yes...as long as the '90 was a V8, you shouldn't have a problem. You might not have a problem even if it's a V6 but I can't say for sure (something about 1 piece vs. 2 piece driveshafts...and I'm not too familiar with 3rd Gens).

 

V6 was the same thing, I know because I own one with a swapped LT1 + T-56 . Also, the 2 piece v6 driveshaft was in the fourth gens.