That's an original 3310 which was rated at 780! It came with a secondary metering block and the original power valves were 10.5 primary and 8.5 secondary. Jets you have are original.

Not familiar with the "lean adjuster".

Most double pumpers do not have a power valve in the secondaries but did have the metering block with jets.

3310-2 and later had a metering plate instead of a block and were rated at 750. Maybe a cost saving measure.

Not 100% sure, but I believe 3310 Holleys were used on some z-28's and/or big block Chevy's as well as being available as an aftermarket performance carb?