I have a 64 valiant slant six push button I would like to leave it push button and put in a 74 slant six motor will this work as I know that there is a difference in the flywheel/flexplate register diameter I thought that I once read that you could go one way or the other but I'm not sure which way!Or is there an other way to get the newer trans to work push button?

The crank "register" got larger starting in 1968.
To use a later (68 and up) SL6 with the early pushbutton trans, you will need to use the later flexplate and get an adaptor ring from Wildcat Wrecking / Ed Yost.
http://www.wildcatmopars.com
The special adaptor ring will press into the larger crank register hole and support the smaller pushbutton torque converter nose. (hub)

Also be sure to swap the oil pan and pick-up tube from the 64 onto the later engine, the sump is in a different location.
DD