The 402 style torque arm crossmember will normally work with factory exhaust, aftermarket y-pipes that connect to the factory exhaust manifolds and aftermarket shorty headers and y-pipe set ups. The 405 style torque arm crossmember is for aftermarket long tube headers and y-pipe set ups and provides around 2" more exhaust clearance.
Some long tube header y-pipes will clear the 402 style torque arm crossmember. If you want to check you can lay a straight edge across your tunnel brace mounts spaced down 3/8" off of the floor mounts. That would be the top of the 402 style torque arm crossmember.
Another common question we get is if the 405 long tube style torque arm crossmember can be used with regular exhaust for now until the customer then upgrades to long tube headers down the road. The answer is yes, with one exception. If you get the 405 style torque arm with a front driveshaft safety loop, the front loop will rub against the factory y-pipe. So if you have the factory 1998-2002 F-Body y-pipe you can not use the 405 with a front loop. If you are not getting a front loop then it will work fine.
The 405 style torque arm crossmember (with or without a front driveshaft safety loop) will work fine with aftermarket y-pipes that connect to the factory exhaust manifolds and aftermarket shorty headers and y-pipe set ups, you'll just have more exhaust clearance then you need and will be good to go when/if you upgrade to a long tube headers and y-pipe set up later.