1990 Cadillic Seville you want to convert it to a stick what parts can you use or make work PS don't laught?

As this car never came with a manual transmission, you cannot get parts from a donor car. Even if you could the task is daunting. But in your case, you will need to do lots of fabricating, as you won't be able to find any parts that will fit without major modifications. I am not laughing, but you either better have lots of money or lots of skill.

transverse is a engine mounted sideways...

if you are using your original engine, determine whether your engine is transversed or not, find a donor car with the same configuration. locate a donor with similar block type and remove trans, clutch, etc., you may want to aquire the cv axles for modifications at a speed shop if you are working with FWD, or the drive shaft if RWD.IN MOST CASES, IT SHOULD SWAP EASILY 60-40%...