Exhaust valves, Ti or S.S.

[taggart]

I have a 800, I don't know what year it is, I has the RER, the only numbers on the block 0001923 nothing else. I have two sets of exhaust valves, one set are Stainless steel, the other are Titanium. I've heard mixed remarks on the Ti valves, dose anyone have any input on them? and what they might be worth? or on how I can find out what year this 800 is?
Thanks