I can't imagine it has anything to do with your manifold.

The cyl.pos. sensor lives in the distributor, & several people have said you can't buy them unless you buy the whole distributor. So you might want to start looking for loose or broken wiring at the distributor, or corrosion in the connections?? Good luck, I hope it's that easy.

When you jumper the SCS connector, the light flashes the code repeatedly. Do you know the difference between a code 9 vs. a code 1 that keeps repeating?