The thermal paste you have with the Orb will be fine. Arctic silver is good but there's probably only a couple of degrees difference between that and what you have (at a guess).
Can you link to the Blue Orb so I can see the brackets you refer to. If they don't have a push pin then the motherboard will probably have to be removed. As it's an old design I hope it isn't the even worse socket 478 mounting than the push pin one is.
Isopropyl Alcohol is perfect for cleaning.