As an owner of a dual carbed 261 with Fentons like you are considering, the first thing I suggest is sell the leak-chesters. I too had these on my initial setup and got tired of cleaning up the leaks.
I replaced them with Carter YF's, they are a direct plug in, you don't have to change linkages or fuel lines. Like mentioned above, you need to either buy rebuild carbs together or send them to be rebuilt together. Its important that you mention that you are running duals to make sure they are identical.
Once you have two identical carbs, you need to spend time getting them to play nicely together. First and foremost, your engine needs to be in tune already. Trying to solve an issue with dual carbs just adds variables and make things harder.
Purchase a uni-syn tool, you can get these for short money on eBay. Install the carbs and use the tool to get them set alike, drive it around and see if you have any hesitation. This process will take time. I found that my final adjustments were done by starting the engine warm and adjusting the carbs with the linkages loose, then snugging the linkages. Ever since I have done that, I havent had to touch them.
