I converted mine with the hitec module and when I run twin elevator servos I use ch 2 then into ch 8 and just activate 8. The other way I have done it is go into an open port like ch 5 and use a P mix and slave ch 5 to ch 2.
I have zero understanding of the Spektrum or JR conversion though but a couple of guys at the field have gone with the JR because of the selection of RXs. My radio operates exactly the same as it always has with the Hitec system.