love the old girl

I was driving my dads and my 64 4 door valiant arouned and i forgot how much fun that car is. Just a slant 6 but it runs great. You would be suprised how sideways you could get a old valiant(on the dirt). We are someday going to put a 318 or 360 in it. What do you recomend 318 or 360? If it is a 318 we were going/hoping to get one from a junked car and rebuild it. Can i use the stock tranny from the slant? it is a push button tranny. how do i lower this car? i am use to aircooled VWs.