You could look at capping that morning nap to around 30 mins and see if he'll take the afternoon nap sooner?
Alternatively if you feel he can cope with a bit of OT for a while you could jump CT to one nap. So you set nap and BT, hold for a week and see how he does. The idea with set nap and BT is that you try and regulate their day and timings. BT could be up to 30 mins earlier in a case of a short nap, but otherwise you try and stick to the times. More often than not after a couple of week the timings need to be shifted a bit. For example for mine, I needed to move the nap out a little and once she was napping well she reverted back to her 11hrs ONS after a month or so.
If you were to go this route, I would attempt the nap to be at 12pm with your 7pm wu considering he's doing an hour UT nap at 11am anyway, then set BT at 7 or 7.30pm for a while (again, this may need to be shifted later on, but gives them chance for extra sleep if needs be). Currently he's getting 2hrs sleep a day and 11hrs ONS so I would expect once he settles into the new routine, he'll revert back to that. Does that make sense? Wdyt?