Arline's death occurs when Richard is still working at Los Alamos this is written in "Surely You're Joking Mr. Feynman". When Richard returns to work his colleagues think he is crazy because his wife has just died and he is working.
The scene where Richard breaks down after seeing the dress is supposed to have happened before he comes home and happens because he realizes that he has caught himself thinking about Arline in the present when she has passed on. This is mentioned in "Surely You're Joking Mr. Feynman", .
The gate scene at Los Alamos is accurate and Richard had many more pranks that he pulled while working there. Most notably he picked locks. The one unique combination of locks was a series of file cabinets in a mathematicians office where the combinations began with the first few digits of the natural logarithm of e.
Richard Feynman: Mathematics is a language. It's very difficult. It's subtle. You couldn't say those things any other way - and I can talk to dead people with it. I talk to Copernicus every day.