I'd bet they are lighter than your fixed rib unsingle. My 34 is marked 1.330KG which seems like a really low number compared to what is seen on many other guns but I also do like the way it feels and points. Maybe check if your barrel is marked for weight.
My 34" unsingle w/ adj rib weighs in at KG 1.330 as well. I also have a 32" fixed rib unsingle 680 barrel tipping the scale at KG 1.620. Not alot of difference in the weight for the difference in price!$$