All this talk of Jake going to prop is not accurate. Just because there are two props on a list and one lock, does not mean you can only have one player performing a lock forward role. They are both playing 13 when on the field...in fact, you could argue that Walker is the prop because Jake T still defends closest to the middle with Croker. They both take hit ups and both use the ball as a link man.
As for comparisons with Murray, they are different players. I think Jake is better at ball playing and stiffening up the middle defence, whilst Murray obviously has better footwork and a tendency to poke his head through and get a quick play-the-ball. Both are valuable to their respective sides and if you swapped one for another, you'd be gaining one thing and losing another.