[Arran]

Try using dot 3 brake fluid to get the paint off the knobs, people have used that to get paint off of polystyrene and lucite with no ill effects. In all honesty soaking them in water may get the latex paint off. I think the knobs on these were made out of Tenite II, the improved version of Tenite that does not warp, shrink, and disintegrate. They are very similar to the knobs used on a 46-1201 and several other sets. I have two so called "Hippo" sets, one is white and has a tuned RF amplifier stage, the other is brown Bakelite and has a 14AF7 mixer-oscillator and an extra IF amplifier stage. They are decent sets but people often make the mistake of paying too much for them thinking that they must be rare, which they are not.
Regards
Arran