I've been doing this type of thing with model kits and slot car bodies for more years than I'd like to admit. I have tried the method Steve suggested in the past with mixed results.
Here is what I've concluded.
1. Remember that clear parts because of their formulation will always be more brittle than parts molded in color. This makes them much more prone to splitting and cracking.
2. Because of formulation and age (50+) some colors of plastic ( like Aurora Tan ) can become extremely brittle. Just one drop and they can shatter into pieces. No way to get around this. I don't know every color and brand that are affected, but you will find out when you start to rework some bodies.
3. Most glues used back then actually melted the plastic to weld the pieces together. Sometimes you get lucky and they used some kind of glue that did not melt the plastic. These will usually come apart with a warm water soaking.
4. Headlight lenses are the most difficult to remove because they thin at the edges and usually do not come out whole. If you do get them out they are difficult to clean up.
5. You can use the back of a brand new #11 X-Acto blade to score the lines between parts. This is like eating a Tootsie pop. The temptation is to do it in 3 bites. It takes much time and patience to get good results.
6. Clear parts can be sanded and polished with a good kit starting at 12000 grit "paper"
7. In the end, it is probably best to keep checking Ebay etc. for a clean unassembled body. Only saying this because I tortured myself for years with this stuff. Prices are coming down. Years ago I was selling unbuilt Monogram Lola bodies for up to $140. If you search you may be able to get one under $40 now. Depends on how much time you want to devote to the resto.
This is my take, your results may vary.