Which HMS Vanguard is your ship, 1748 or 1787? If the latter, the below can be found on the Wiki Commons site in high res or at RMG in low resolution. You can use it to make a template to see if the hull is correct. It looks like the bow shape is pretty close but the grating is wrong when compared to the contemporary drawings. IF that is the case, you may be better off making a new grating platform.
Allan
Upper deck for HMS Brunswick 1790 that may help you with the shape.
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'Venerable'_(1784);_'Victorious'_(1785);_'Hannibal'_(1786);_'Theseus'_(1786)_
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The red lines show the shape of the bow on the contemporary drawing overlaid onto your photo. I know things are askew but it may give you an idea of what to do.
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