I've got an 87 33 egg with some of the original Groco Thru hulls. They have the double knob, where you have to loosen the lever on one side to release the lever on the other , to open and close.. These have 2 bolts going down thru the hull too... what's the best way to remove these.. The replacement I know how to do..

From the outside of the hull take a four inch grinder and cut an X across on the outside of the hull. Once complete take a flat chisel and fold the pie shape to the inside, break off with pliers. Repeat around the stem then drive the stem through the hull, replace the through hull and smile at the yard folks because this is what they do and charge alot of money for

Just like Choo Choo said. I redid all of mine a few years back and I had to cut most of the valves with a sawzall.

Your not going to like this, but you have to clean all the bottom paint from around the area first. Then from inside try to break the nuts free, if not than cut them off. Then with a long beefy punch pound the bolts down and out through the hull. Sounds easy in theory, but that's why the yards get the big bucks to do this job. If you have lots of "on the hard time" then take your time.