Thank you to @Byron @AJ356 and @Ichthys for your posts in this thread. Very useful to hear about your different experiences.
It seems like my best chance for a pair is to observe them in the store tank for a while if I can.
You may have to speculate here Byron, but do you think that the outcome would be different if they had both been introduced to the tank at the same time, if they were not paired but in the same store tank?
So to recap a little bit, and please correct me if I am misunderstanding:
A pair of bolivian rams that are friendly towards each other, should be okay to keep in a 280L planted tank with some small schooling fish, an ancistrus and some corydoras?
(I only own the schooling fish so far, but I'd like to have the other three if I can.)
Read the profile on Seriously Fish. The observations are indicative of how this cichlid lives. What we are talking about here is internal behaviours, and they have very little if anything to do with how the tank is set up, barring the obvious issues. The fish are the way they are. Now, some may decide this more than others. In my view this is a wonderful cichlid as a solitary cichlid member in a community tank.
Two fish may accept each other and live in harmony. Or they may not.