If you only see SA signs at sleep periods, then it's probably not SA. If he's clingy ALL the time it *may* be SA, or may simply be a sign that those evil molars are starting to come in!
the way the 2-1 nap switch works is we try to make the PM nap the long one, and we slowly shorten the AM nap. The reason we do this is 2 fold:
1) At around this age, babies start to refuse PM naps if they've had too much sleep in the AM. so, by keeping AM nap short we preserve PM nap; and
2) A longer PM nap helps make it less likely that he's OT at bedtime. A shorty PM nap can lead to OT and then lots of NWs or EWs. Esp. during the 2-1 nap switch as they increase their As really quickly.
Since he's crying at nap time, I suspect one or two reasons: 1) he needs to extend A time, or 2) he's teething and uncomfortable.
I'd probably try making nap a bit later (tho his As are def. reasonable for his age right now) first, and if that doesn't work then I might try medicating before nap and see if that helps.
Try 4 hours prior to nap 1 and limit to 1 hour and see if that works.
Now, if he's only crying before PM nap, then I'd leave Nap #1 time the same but still limit to 1 hour.
The fact that he's having NWs and EWs and putting himself back to sleep suggests to me that he's uncomfortable, and this is the prime age for teeth.