I have a sig Extra 300 sx which has split elevators. Question do I have to connect a servo reverser or can I achieve this with my radio ( Futaba 8uaf super ) by using channel 2 and 8 and reversing one channel?

Yes. I do this all the time without using a reverser. In fact -- the one time I did use a reversig Y it almost didn't end well. [:'(]

Thanks Galen,
I thought that it should be possible.