If it was me, yes. You will have your coolant drained and it would be a good time to do the timing belts and check all the valve clearances, etc. You will sleep better if you go ahead and do them both at the same time so you won't worry about the other side going out at any time. Just my opinion. Paul
I would go with both - I made the mistake of only doing one on my bike -250 miles later - had to tear it all down & do the other one. What would have been maybe another 1/2 hour labour turned into another 3 hour job ( at least for me ) . It's likely that both the head gaskets are 30 years old - how much longer will one go than the other?