Hi David,
I take it you live in NZ?. Not sure what the Law is over there.
You cannot put 27mhz Xtals in a 35Mhz Tx,with all the 2.4Gig sets coming down in price that may be the cheapest way to go.
If you just have 1 Boat using 2 Channels then you could buy an Acoms Tx or similar for £9.00, and a Rx for around £12.00 plus the price of a pair of Xtals £8.00.
Hope this is of some help.
Regards,
Len