I too follow that book, it was a life-saver when my little girl was still waking to nurse 4 times a night at 8 months old! My girl too gave up the after noon nap first, right about the same age as your son is doing it now (she is 16 months today) . Sometimes, I still get two actual naps, depending on how active our day is, sometimes we get one and a rest period og playing in her crib like you are having, and sometimes, we just have one longer nap. It all depends on the day, and whether she is having a growth spurt or not, and I just go with the flow - if she needs 2 naps, so be it, and if not, no biggie. What I try to do is push her morning nap back a little, by keeping her very active until 10am or so, then she will usually sleep until 12:30-1:00. But if she is really acting tired and crabby earlier, we will put her down for an earlier morning nap, and then try another in the later afternoon between 2 and 3. Also, if she takes only the one nap, she will et tired earlier in the evening, I just put her down a little earlier; our usualy bedtime is 6:30 (and she usually sleeps through the night til 7 am or later) so on a tired night I might push it up till 6:00. I just follow her cues, and let her decide when to go to bed. Usually, if she is yawning and acting sleepy, I ask her if she wants to go up to bed, and she will run to the gate at the bottom of the stairs and say UP!
Good Luck, let him lead you to what he needs!
Jess