I have an 85 camaro. I'm building a 383 stroker motor. Actually all ready built and in the car. The motor has  KB flat tops, Vortec heads, Aluminum intake, Holley 750, Eagle floating rotating assembly, Lunati 477 cam. Drivetrain has a 700R4 with a shift kit, corvette servo, and hi performance sprag, also a 1200 stall (too small i think?). I have a set of headers that i ran on stock heads but they are too small to cover the vortec ports. Any suggestion on headers? Also side pipes for the car? Also if there are any performance tips you can offer i'd appreciate any info.  

Check out these commercial adapter plates at this URL.

http://www.rehermorrison.com/items/Header%20Flanges%20Adapters.htm

This may offer the solution or give you an idea for your own fabrication. The Morrison site suggests cutting off your existing mounting flange which is OK if you have a welder; but you could use these as an adapter and just sandwich them between the head and header flange. The adapter could be modified with a grinder to enlarge the opening to fit the Vortec head's ports and the other side to match your headers.

It's important to provide a situation where the flange against the head either matches the port smoothly or is slightly larger. It is devastating to flow if the flange hole is smaller than the port.

Bogie