Have you verified that it doesn't have an integral head?
1974 was the last non-integrated year for the 250, and it did have a 2" exhaust manifold with a 2-bolt flange. After that, the 292 exhaust and two versions of the 250 integrated had a 2.25" with 3-bolt flange that are both angled downward to gun under the oil pan to the passenger side (as opposed to the angled exhaust that runs under the driver's side). The exception is the HD 292 which has the 2.5" manifold, and the 1979 Camaro, Nova, and Caprice 250 that got a non-integrated head along with the SD 292 exhaust manifold.
