So the short, unhelp answer is "Not Much"!
(I am interested in the opposite; adding Blood and Plunder figures to the rest of my stuff

)
There are a few figure comparisons around, which help a bit. These are the best two I think

From the left: Warlord ECW, Warlord Marlburian, B&P, Black
Scorpion, Galloping Major

From the left: ??, Warlord ECW, B&P, Northstar 1672
So the Front-rank late 17th C/WSS, and the Northstar 1672 range will work. I would put money on the Bicorne ECW figures and Renegade ECW figures (now sadly OOP) fitting too as they are the same size as Frontrank. Probably the Bloody miniatures ECW range too as it is 100% compatible with Bicorne/Renegade - see the comparison here -
https://www.bloodyminiatures.co.uk/gallery?pgid=l2ouh1wj-888ad5af-4434-40bb-a437-002e1bb4f7e0Redoubt and 1st Corps also do tall ECW figures who will probably also fit