If you want overdrive in a mopar try the 518(727 with od) swap. That way you can use your existing shifter and kickdown and have a lot stronger trans. I'm doing one behind my 408 stroker. Info at the patc trans site. The switchs they use are for a chevy 350 trans 3 gear clutch are sell for about $5 at the trans supply. The vacuum switch is from a mid 80s caprice and is called a od control. You can pick them and the attached wiring at the junkyard cheap.