904 for 408?

The Trans-go TF-2 kit is a great kit and will make it shift firmer but it won't make it shift real hard but since it's for your parents you might want to just use the TF-1 kit. I haven't used it but it's supposed to be milder. Considering the driving style (not being raced and no crazy hp) the 904 will due just fine with a mild shift kit. 3.23's should work good unless your running a real short 14" tire in which case you might want to consider using a 2.76 or 2.94 gear. When you decide what gear you will run give all the specs to a good converter company and have one made specific for the application. Will work much much better than an off the shelf converter. Sounds like it will be a real neat sleeper when your done.