I've been working on LD with the same combination in mind of Remorseful Cleric and Fall of the Thran in different shells.
This is what I've come up with so far.
Disclaimer: As this was the first time I've really worked on Boros and Azorius, these decks suffer from lack of rare lands. That will change asap.

Boros Creatures
Can be fun to play but not so focused. Creature based stall/maybe win.

3 x Fall of the Thran
7 x Mountain
3 x Remorseful Cleric
2 x Hero of Precinct One
2 x Rekindling Phoenix
8 x Plains
1 x Clifftop Retreat
2 x Sacred Foundry
3 x Boros Challenger
2 x Tajic, Legion's Edge
2 x Deafening Clarion
3 x Truefire Captain
3 x Heroic Reinforcements
2 x Cleansing Nova
2 x Lyra Dawnbringer
3 x Healer's Hawk
1 x Star of Extinction
3 x Shock
3 x Lightning Strike
1 x Lava Coil
2 x Evolving Wilds
2 x Boros Guildgate


Boros Burn
More focused way to get to combo with fatty finishers.

4 x Shivan Fire
9 x Plains
4 x Shock
4 x Lava Coil
4 x Lightning Strike
2 x Sacred Foundry
2 x Stone Quarry
1 x Clifftop Retreat
4 x Deafening Clarion
9 x Mountain
3 x Remorseful Cleric
2 x Cleansing Nova
3 x Fall of the Thran
2 x Rekindling Phoenix
2 x Lyra Dawnbringer
2 x Angel of Grace
3 x Revitalize


Azorius
Different way to look at getting to the combo and finishing

3 x Remorseful Cleric
11 x Plains
3 x Fall of the Thran
2 x Cleansing Nova
2 x Lyra Dawnbringer
2 x Angel of Grace
3 x Revitalize
3 x Spell Pierce
7 x Island
2 x Search for Azcanta
3 x Sinister Sabotage
2 x Divination
2 x Syncopate
2 x Glacial Fortress
1 x Teferi, Hero of Dominaria
1 x Teferi, Hero of Dominaria
3 x Conclave Tribunal
2 x Ixalan's Binding
2 x Chemister's Insight
2 x Memorial to Genius
2 x Meandering River

Another combo to maybe think about is fall of thran with mending of dominaria, bit slower that what you're doing mind.

I just had an immaculate game with the Azorius version.
Lots of Immortal Suns and Angels and Nova's running around. Lot's of countermagic and draw and removal on all sides.
Fun game. I finally got to the point when I could easily stick the combo and did.
Coming to YT and here soon are the last final minutes of that game.

So first you win the game, then you play your combo?

Hehehe.
Nope. Stall/imprison/wipe the board out, combo, start winning, win.
The Azorius version is by far superior. It's now -1 Meandering +1 Hallowed
I'll pulled the combo seven times in a row now for six wins before the Cascade event drew my attention away.
In the above video I was losing the game badly most of it. I had to stall, wipe, lose three angels (that was my second Lyra) and use Teferi's second ability on the 8/8 that makes tokens at upkeep before I started recording.
There are some games where I am winning it seems before the combo but pretty much guaranteed after I do.

This was a LONG game:

Why not play mana dorks to ramp into the 6-cost spell?

I have thought about it and it's a possibility. I pretty much put the deck down this weekend to concentrated on the Cascade event. Will be running it some more today and maybe rolling into a Bant variation. Obviously the best shell for the combo is a work in progress.