You might investigate rc-dymond.com
I saw an ad in a model magazine for their Futaba compatible 2.4g upgrades and receivers so I sent them an inquiry. Here is a partial quote of their reply:

We have one Futaba FASST compatible receiver $ 59 # 80551.

8 channels and extended range, comparable and tested even better than
some of their high end products. Tested by Red Scholefield
Our other 2.4 Ghz conversions for existing 72 Radios are not interchangeable, but
have full range as well.
If you want to have a catalog with detailed information, please send me your snail mail address and I will send you a copy.
Helmut

I haven't investigated further as yet so don't know the quality of their product.

Good luck,
=Rick=