Hi Brian

No need to put an extra shim on your engine, it will run perfectly like this!
The b11 is a really good engine, you won't be disappointed! You can buy the combo B11 with pipe and header, it comes with the new 2087P pipe and 198P manifold which is a really good in-between. For more bottom end, you can go for the 204P manifold, but still the same pipe.
As for the reducer, 7 is a good combination, as the fuel economy is awesome, so you don't need to go lower! I would also recommend to try the oval venturi, for more bottom end and even better mileage.
As for the refueling, as soon as the engine will ok (not too rich) in the bottom, and mechanic don't put fuel on the pipe, you will be fine!! I advise to do a small protection on your body between the tank and the pipe, really useful in summer!
Enjoy!

Reno