if they are using a Mopar production block then again it is comp hehehe
“The engine actually uses a Mopar production block and that’s its weakest link. It’s the best naturally-aspirated platform on the planet, Mopar stopped production and some of the blocks are just not good. We went through four blocks before we found this one. We’re not on the ragged edge with it yet because we’ve struggled with the tune-up from the block issues. A lot of the data we got earlier was skewed from the block’s shortcomings.”

https://www.dragzine.com/news/book-racing-engines-smashes-nhra-small-block-na-record/

They must have a loose definition of "production block", I always thought a "production block" was a block built for a "production car". That means it was a block issued in a running driving car from the factory assembly line or an exact replacement block.

I don't know about altered, but more than one car in Comp Eliminator have billet blocks.

My guess is that they run the GXP because they had one. To sell the GXP and built a Dart probably would have set them back a lot of money.

I don't think you could call Mr. Brook or the folks that run this car Mopar loyalists, they just want to go fast, and they are!

You are right Brandon wanted to set new records has worked with pro stock in Australia for a few years Bob Brooks wanted Brandon to run his motor.
I talked to Brandon last year about running a mopar motor his answer "I don't care two sheets about what power plant I run it's faster than my Chevy motor".
I was watching that pass you could tell it was on a great run.
Everyone was cheering and giving each other high fives