You should use a GWS crystal in a GWS receiver, not a Futaba crystal. Now, it may very well be that the GWS and Futaba duel conversion crystals are compatible, but unless you know that for sure, match the RX and RX crystal brands.

That said, when dealing with FM, any RX on the same channel with the same "shift" will work with your transmitter. There are lots of options from Hitec, FMA, and many others that will work quite well with your Transmitter.

"Shift" is the direction the FM signal is modulated. In the US, Futaba and Hitec shift one way, JR and Airtronics shift the other. I've heard that in Europe that isn't the case, and you can even use JR and Airtronics RXs with your Futaba TX, though I haven't seen that verified. The result being that in the US, RXs are labeled as either "JR/Airtronics compatible" or "Futaba/Hitec" compatible.

Some RX's are shiftable, and can work with any FM Transmitter, Hitec and a few other companies make some.