Actually, that's a Stahl type header flange. The adapter is a three piece part that bolts to the head at each end exhaust port, and across the center two. There are many versions of that bolt pattern header flange...Stahl is only one. There are many SBC head versions that have that bolt pattern, and don't need an adapter. One of the main differences is in the center two ex ports. The Stahl will fit most standard port heads, where the center two ports are closer to eachother. (You'll notice how close they are in the above header flange) Then there's the spread port head, where the two center ex ports are further apart. Typically, spread port heads won't need an adapter, as they're the ones with the bolt pattern already in the head.
Just some SBC trivia. These are just a few:
Brodix -12
http://www.secureperformanceorder.co...es/4200514.jpg
Dart 18*
http://www.secureperformanceorder.co...es/4300554.jpg
SBC, 15/18 degree Rehr Morrison (non spread port)
http://www.secureperformanceorder.co...es/4370515.jpg
SBC spread port 1 7/8"
http://www.secureperformanceorder.co...es/4200534.jpg
Stahl round 1 7/8"
http://www.secureperformanceorder.co...es/4101514.jpg
Stahl rect. 1 7/8"
http://www.secureperformanceorder.co...es/4102514.jpg