Maybe those grips are worth saving. One way to slide them off is to get an open ended wrench that will just fit over the handlebars on the the inside of the grip, then take a mallet or hammer and tap the wrench to pop it off. I've used an adjustable wrench also.
Very nice find! Those grips look to be cooked on. Doubt you can remove them without cutting them off. The foam grips above are really nice and I have put them on a couple of my bikes. Very comfortable!