Whatever you do, if your Hedmans have the oval port design, you MUST use the gaskets designed for the oval ports.  If you use rectangular port gaskets, you will have 32 exhaust leaks, 4 at each port.

The best thing to keep header bolts tight is a good lockwasher and a solid H-pipe or X-pipe or whatever method you can use to tie both pipes together so they fit the engine as a non-flexible unit, instead of individual pipes that cause the headers to pivot against the gaskets at the head ports.

jeremy's post reminded me...  I had the aluminum collector gaskets and had small leaks, but could have been caused by road rash on the flanges.

I was using copper gaskets at the top and they were on for many years with no leaks.

Be sure to have an H-pipe or crossover pipe below to keep the headers from rocking.