3310's can be either a 4150 or 4160- difference is (mainly) in whether there's a metering "block" for the 2'ndary side or a metering "plate".
A metering block-equipped 3310 (4150-style) will have the same size metering block in the back as it has in the front. This is located between the float bowl and the body of the carb, a metering block is about 3/4" thick, give or take.
I would be replacing that 15-year-old power valve, if it were me. It doesn't need to leak to be bad- once they're gas-soaked than allowed to dry out, they can become stiff and less responsive to manifold vacuum than it should be.