The reason that you have trouble using the Futaba R-114 is two fold: The sync pause/reset time for the earlier systems was different, as was the frame rate. Changing the sync cap in the decoder will solve that. Additionally, the Futaba receiver outputs a positive pulse to the servo. Some of the early systems used a negative pulse to the servo, so a pulse inverster would be needed...Ace R/C used to sell them. The other option would be to get a Receiver crystal that was cut 455 Khz higher that the channel frequecy for the Futaba(high side as opposed to low side crystal) to invert the pulse train going to the decoder.
I was thinking a bit about this Jay, I don't think changing the crystal frequency from low to high side would have any effect on the decoder output (ie. changing negative pulse to positive). However it should be a simple task to find the AM detector diode and reversing it to do pulse transformation.
On the other hand it's early in the morning and I'm not really awake yet.