Granted I know very little bout metallurgy,
Same here and even my rules of thumb might be a bit dated and/or not apply here. Maybe someone a bit knowledgeable will explain this soon.
but if that is the case with copper, why would Triumph use copper gaskets on the exhaust ports?
Because they are cheap and maintain the seal well under heat and Triumph factory likes all things cheap?
I guess this link is close enough to what I ment:
The further away the two metals are on the table the more likely the galvanic corrosion.
Now that I refreshed my memory a bit more, I think the anode-cathode size ratio played some role in this also, so the aluminium block being large and copper gasket small...humm... yes, maybe it's best to wait for the explanation from someone who actually knows what they are talking about.
Until then, I am sticking to my aluminium based thread lube.