What is the diff. between high/low band.

I just got a Futaba FP-R127DF. It had a #16 Crystal but I would like to use a #26 or something in the fortys. will this work. Also I have access to a Futaba tx that had a #42 Crystal but the guy who has it says he thinks it's a high band tx. Will this not work?

Thanks in advance.

Del