Standard gearbox vs. weedless gearbox

[HurtLocker]

I have a 1974 4hp light twin that has a weedless gearbox. Is there a speed difference between the two gearboxes? I want to use mine as a kicker for trolling on Lake Michigan (pushing a 16' Sylvan) and I have to run it at 3/4 throttle just to get 2 mph going w/waves and current. Any thoughts?

[boats.net]

I believe they were same gear ratio.