Not a problem. I'm also 6'4" and after reading the BA literature started to worry about my future. This resulted in me sending letters to every airline I could get an address for (UK only). Out of all the replies BA was the only one with a restriction. Several of the replies from other airlines stated heights of flight crew members as 6'6" and 6'7". So relax, carry on training and work for a company that selects pilots on ability and not uniform size.
Happy Landings
