Despite Fred stating he had smoked 2 packs a day since he was 10 and having a clean bill of health (highly unlikely), he was never shown smoking in any episodes before this one or for the rest of the show's run.
When Fred opens the drawer that contains all of his glasses, he begins to clearly put on a pair of wire rimmed glasses to read the letter. When they cut to Lamont and then back to Fred he has a different pair on.
Lamont says the amount of cigarettes Fred smoked in his life equals 41 miles or the distance from their place (9114 South Central Ave, LA) to Disneyland. The distance is in fact just over 42 km or just over 26 mi.