I'm gonna go out on a limb and assume it's not still printed on the bottom of the battery hatch?
I had one several years ago.. (the old 72 Mhz radio and Brushed motor) but pulled the old receiver out long ago..
I don't recall if the frequency was printed anywhere on the receiver or crystal though.
I do still have the TX, which you are welcome to (you'd need to pick up the shipping costs)
you COULD do like I did and just pull the receiver and go 2.4 gHz of course