the century is the same body as a regal gs , buy a wrecked regal gs or gtp parts/donor car and swap the sc 3800 into it - they are stupid easy to mod , headers , pulley , tune will put you low to mid 13's ,add an intercooler & rockers would be solid 12's as would cam and e85.. a few sc cars running 11's , turbo/intercool if you want faster than that , 8.6 @159 is the quickest stock block/ rotating assembly 3800 s2
or you could turbo the 3100 I have seen post with people doing it with great results but its not as durable as the 3800 nor is there as many enthusiasts to help you figure out the best combo as there are for 3800 powered w bodies