https://worldofwarcraft.com/en-us/character/us/blackwing-lair/unkillabull
Replace the Talasite gems with 2 strength/2 stamina or 2s/2h
Pally is quite insane. I block 40% of all attacks. With high haste you can chain Blessed Hammer together almost infinitely, so you constantly reduced an attack by 74. This is fairly nuts vs PvE targets. It also gens Holy Power, so you can chain like 8 Shield of the Righteous, which takes armor mitigation from 40% to 60%. Concentration reduces damage by another 18%.
Mast>Haste>Crit
I like the shield to belt over the heal because a. the heal is only 400 outside BG and b. attacks are mitigated by your block/armor/vers/concentration before being applied to your 250 damage absorb, so it last for a long time. It can blow up and taunt things though, so it's a last resort. The heal would be fine here as well.
Trinkets you have tons of great options, if you run with a pug heal that isn't paying attention Paj is amazing and gives you it's full 1670 heal outside BG.
When Crusader is fixed it would be worth trying to trade glitch Naga Hide to a BoE wep, unsure if it's possible though.
Check out
https://www.wowhead.com/item=119449/shadowberry as well.
I'd probably run
https://www.wowhead.com/item=12645/thorium-shield-spike if I could, it's 9 damage but it's 100% chance on block and adds up vs tons of targets.
I think next best option would be Warrior... but kind of a guess. I believe the 20% damage reduction from Protection stance is still built into the spec somewhere but my info might be hella old. They also seem to be able to take more damage, even over other plate classes. But you can't beat Pally emergency heals for pug content.