The Marines would normally be placed in the fighting-tops (hence the name!), the squarish platform at the top of the lower part of the masts. Unfortunately this is a highly complex area, you have the top of the lower mast, the heel of the topmast, the crosstrees and the fighting top itself, plus there is a large quantity of rigging. In order to do it right you need quite a bit more than a picture.
Something like James Lees' "Masting and Rigging" would give you all the info you need to get it right.
https://www.amazon.com/Masting-Rigging-English-Ships-1625-1860/dp/0870219480