I have a similar vintage NC33 Mk2 and I have refurbished the forward toe rails. The structure consists of two vertical pieces of teak either side of the GRP bulwark, a teak capping toe rail, the inboard vertical and the toe rail have an inner packing. This was originally pitch pine. In the course of 40 years most of this will have disintegrated. The “packing” consists of an L shape. The L is 33mm wide at the top, 25mm below the toe rail, and then extends 50mm below the rail and is 10mm wide at this point. I have replaced mine with iroko that was machined in two parts one square bar and the other piece as a shallow L. To remove the toe rails and the supporting timber it is best if the boat out of the water. It is a very strong structure with over 200 screws holding the box section together. You can’t easily remove one side without removing the other. It’s an all or nothing job. I have replaced all the outboard vertical teak, and about 50% of the inboard verticals, all the packing and all the toe rails. There are pairs of 50mm screws that go through the inboard timber, through the packing and into the GRP, and into the outboard timber. However, behind the inboard vertical and packing are further screws that secure the outboard vertical. It is immensely strong but a long patient job to remove it all. I recommend a 10mm Forstener bit, and a sharp 10mm chisel to remove the 200 or so teak plugs over each screw. The screws are probably original. They are slotted phosphor bronze wood screws; many with shear off, on others the heads will just disintegrate. Using a plug cutter I cut around these and then removed them with mole grips once the timber is off and the remains of the screw are exposed.You will need buckets of new A4 stainless screws to reassemble it all. The good news is that you can cold bend the new teak around the bow with heavy sash clamps and a lot of patience. My skills don’t extend to the long scarf joints Sitala used on the verticals so I simply used 45 degree butt joints. The final finish doesn’t end up being very different. Good luck!