Looks like a Delta 1600. Here is a breakdown of the faucet
Here is the cartridge. Readily available at plumbing supply stores.
You do have to be very careful unscrewing the cap nut. You can destroy the valve by breaking 3 little tubes which connect the body to the manifold. This will be a BIG problem.
Try soaking in white vinegar or PB blaster. Try adding heat from a torch, tapping a little, etc. Sometimes it will be necessary to slice through the nut with a dremel. The nut and other parts are still available, so don't fret over damaging it.
Sorry , not able to post links to commercial websites, but you can find the info with a google. Just look for Delta 1600.