i love it, its a great conversion! As far as "advantage" goes, most players i play with use the front of the tank for line of site, not the gun itself. But as long as you and whomever you play come up with an agreement before you start its all cool! Well that is if you are even going to use it on the table top.
While I can really appreciate how you've used the plasticard to give the rhino the "details" of the old-school rhino, I think that many of your opponents might have a problem with the fact that the demolisher cannon placed that high gives a significant advantage over the stock model.