The MoCo of course says it can't be retrofitted. I figure with enough tools, torches, and ingenuity there isn't much that can't be retrofitted to anything, but then the question becomes why bother? The 5.4 gallons in the old tank is more than my butt can stand at one sitting anyway.
Jerry
That's a change that leaves me a bit in the dark also. It's only just over a half gallon more fuel (I know, you're not saying "only a half gallon" when you're out pushing or waiting some night).
The old tank's crossover is a greater hassle for removal (quick couplers in the lines on both bikes means that's not a hassle anymore). Aside from that, however, the new tank requires different seat, different dash, new tools to work on the pump/filter and some other changes. Far more than just getting it bolted down on the bike.