I got a 1991 Oldsmobile Calais with quad 4 and 5 speed manual transmission is it possible to take 1986 Buick century 3800 mount the transmission?

No, it's highly unlikely you can directly mount a 1986 Buick Century 3800's transmission to a 1991 Oldsmobile Calais Quad 4. These are completely different transmissions designed for different engines and drivetrains. The bolt patterns, bell housings, input shafts, and even the overall dimensions will be significantly different.

Even if you could somehow overcome the physical mounting challenges, the internal components (gear ratios, etc.) wouldn't be compatible with the Quad 4 engine's power and torque characteristics, leading to potential damage and poor performance. A significant amount of custom fabrication would be needed, and the engineering required would be far beyond a simple swap. It's not a practical undertaking.