BS11 through BS19 (the ones with the low cloth caps) would make good British marines around the turn of the century.
However, these Front Rank WSS figures are tall and bulky relative to Foundry pirate figures. They look like very big stocky men next to most other 28mm. I have quite a few FR WSS cavalry, and I used to have four 12 figure battalions of the infantry, including one of the grenadier/fusilier/marines in the low cloth cap.
I would suggest buying a couple of the civilian men and an officer or two. These would be OK as big character figures regardless of whether you decide to buy the marines. If you like the size comparison you could then buy some of the marines.