Probably better off with a 6.7. 6.4s are easy to make power, but the 6.7s are coming along quickly. Only downside is that you have to spend 3k on dual curlers before you can do too awful much. Give it time for a couple other shops to come up with dual set ups and the price will go down
Ok cool how are the 6r holding up
there are some disadvantages like dual pumps and rods right off the bat.
But you dont really need to worry about pistons and all the other crap that goes wrong with 6.4s that cost big money.
Morgan will have a drop in pump that will probably be big enough for most peoples needs