Yes the older Ping putters are lighter in weight and there is no sure fire way making it feel the same as the newer putter.
I had tried adding lead tape on the putter head. Weigh inside the hosel. Hosel weight plus lead tape. A heavier shaft, counter weight the shaft with lots of added weight to the head.
I tell you, a putter that feels right is rare. I can put with just about any style of putter including using the leading edge of the wedge, but a "right" putter will be like something you could count on under any circumstances.
Did you, even tried this putter you wanted to buy ? I would ask to check it out to putt it on the real putting surface. Once and for all you will either bite the bullet and take it home or be done with it and not to have it in the back of your mind.
Like they say in the commercial " it's priceless" if it work for you. I like the face it has the special studio putter grip which in itself worth some dough. Find out if this is something you want and THEN offer less than a Franklin to take it home.