Quinquari fit twin rams as standard; we had a problem with one of them on a boat I was driving once so simply removed it and ran on the good one for a few weeks while it was sorted. Worked fine. However I guess this is a good example of why you should have two; in case one fails! (Wonder if having twin rams counts as having alternative steering in in the case of coded boats.)
Either way you'll want a tie bar connecting the two.
I have twin 150's and have the single ram with a tie bar with great results and no problems. Please note that you need the appropriate P/N's and tie bolt for that application but it is well below the 600HP limit.