You can easily fit the stock DR650 fuel tap to an IMS tank. I needed to file out the hole in the tank slightly so the tap body could fit through, but the mounting holes were correct.
You need to take a little out of the corner of the top two cooling fins, but 10 minutes with a dremel or burr in a drill fixes that.
I used the stock tap because I like the vacuumness of it. Means I never forget to turn it off. Though reserve volume is a little less, I only got around 45km on reserve with an IMS 19litre tank and the DR tap.
Vladivostok - Denmark 2008... Finished.
Denmark - South Africa 2010-2011... Finished.