I would just do a 30mins capped nap at 2pm to get him through to his usual BT (when he did nap). We're trialling something very similar atm. We did wu 7 ( usually 6.30), nap 1.45-2.15, BT 7.30 and she's still not quite asleep yet at 8pm today.
Remember the 2-1? That was quite inconsistent for a while, it did settle down though didn't it? That's what I keep telling myself anyway! Some days were 2 naps, sometimes 1, we just have to go with the flow during these transitions don't we?
Yours is doing really well with the NND's it seems, maybe just the odd catch up 30 mins nap here and there might see him through? We did that with the 2-1... A short CN here and there to keep OT at bay! At least yours will pull a decent night, the max we've had here is 11hrs on a NND! Xx