The engine needs to be set up to where you can completely close the main throttle barrel with the servo.

I set mine so that with the stick full back and the trim full forward, its just right for starting at a high idle. It has usually worked out (most times...) so that the engine will idle as low as 1/2 trim and minimal stick.

With that set up, I can positively shut down the engine whenerver I want.

There's several options for fuel line access.
I've seen people route the brass fuel line from the tank pickup out the side of the plane, and then a 1/2 inch break and another piece of brass tube going on toward the engine. Short pieces of silicone fuel line make the connections. (A picture wold help... but I don't have one. )
The commercial "Fuel Filler" valves allmost all seem to have leakage problems after a couple of months of use...
Then there's the 3 line tank system, where you route a 3rd line (a second clunk or a second vent... your preference) to a convenient location and disguise the plug as some detail of the model, such as a gub battel on a warbird... or a pitot tube...
Ant the favorite of many Patten flyers is the "Fuel Dot" which is essentially a commercial version of the hidden 3rd line.