I don't use a chisel for those lock plates, it's too wide. I just get a cheap flathead screwdriver and use it as a drift down the retaining grooves to pound in the lock plate tangs.

This usually destroys the lock plate, so you'll definitely need new ones before starting. Having said that, I have had success at pounding them back in to shape, even after my traumatic removal method. I wouldn't recommend it, but in an emergency, I'd suspect you could drive around for a little while before replacing those plates.