The 401 is the perfect gyro for the T-Rex and works just ifne with JR radios. I have 1 in my T-Rex and 1 in my Raptor 50 both flown with a JR 8103. You simply trim the connector a bit and it fits right into JR Rx's. Of which I am using the 770 and 649.

This is not a problem, get the 401. You'll be glad you did. Oh and get the Futaba 9650 to go with it they are a perfect match.