Usualy it is OK to connect 3.3V logic to 5V logic, because TTL high is from ~2.4-5V So if you have high 3.3V it will be detected as High. If it does not work, You can use pull up rezistors. Another posibility is tu use logic buffers - you feed them from 5V sources, and input 3.3V and you have 5V in output ;)

Have fun :)