There is a whole community that AutoCrosses these GM cars.
Performance parts are available including Headers.
In IHRA it is either open exhaust stock exhaust manifolds
OR
Mufflers and Cats with Headers.
Oversized stock pistons should be available.
The Crank can be indexed in Pure Stock.
For a Tune you should have ODB-1 PCM.
Contact Bryan Herter for a Tune.
http://www.pcmforless.com/
Torque Converter...you should be able to get one for your ride.
May want to try Yank or Edge converters.
Short Tires are available.
Barry Werner runs HF/SA and has a set.
His little Dodge with a 1.7 VW made engine runs a full second under in 1/8 mile.
On a good day
Also Bullet Cams can build you a IHRA Legal Cams.
Call IHRA and make sure they have the right specs for your application.
Plus LOSING 400 pounds is a huge advantage..
How you do that is another issue..!!
Dan