Changing Carbs, What jets?

Basically -

3310 is a 4160 style carb which doesn't have a secondary metering block

4779 double pumper would be a 4150 style carb because it does have a secondary metering block.

Metering plates are used to save money on initial production. They are cheaper than a block. You can buy and/or modify the plates, but a secondary block is so much easier to tune with.