[TWOOD]

Well, basically. I cut the gasket material to fit the shape of the flange and the exhaust passages and mounting holes.
But, I had to accomodate a gap, between the header flange and the exhaust pipe flange which tapered on one side (of the car) from zero to .035" and on the other side from zero to .100" (on the other side of the car).
Hence, the need to cut the gasket into a half width gasket for the .030" gap side and into two gaskets (1/3 and a 2/3 width pieces)for the .100" side. These were stacked or sandwiched with RTV spread in between each layer to fill the gaps that the gaskets could not.
I don't think that you will find a stock gasket, pre cut to fit, which will accomodate a tapered gap. I supose that I could have had a tapered aluminum shim machined to fil and used two standard stock gaskets or RTV.

Suggestion: I would determine how much gap you have to fill.
Hang the side pipe loosely on the header with it just making contact on which ever edge mates up first. Then measure the gap with a feeler gauge.
That would tell you what you are trying "fill".
Hope that this might have clarified my previous post.