Need advice for fixing my custom offset firebox

[Boar Dane]

Hello,
I’m looking for constructive advice to remedy my recently built custom smoker which is made of block, firebrick and stone exterior. Th problem is my firebox is way too hot the top and it is smoke and expanding upward cracking the exterior mortar joint. I’ve added pictures of the whole unit and the problems. There is a steel plate baffle system under the bluestone top on the firebox with vents, but the bluestone top still heats up to 275 degrees F. Need some masonry advice.
Many thanks for any advice. Sorry some pictures are not straight

 

[Smoked&Baked]

Please note: I know nearly nothing about this stuff and someone will likely come along who knows a lot about it and laugh at my question

Was it built worth refractory mortar? The stuff you use with fire bricks? If it's getting that hot I think it needs it?

Edit to add - looks awesome BTW!

 

[bschoen]

Second the refractory mortar, also you need to let it completely cure out before use.

 

[1MoreFord]

Also when you fire it the first Few times you build Small fires to complete the final cure of the mortar. Gradually build the fires larger.