I see Challenger RTA has a blackhawk frame dimensions book also! Yes that's my reference spec.
I laid out the 8 vertical post with large washers at stop points to hold at the right height.
Then slid it up under and non crashed car to confirm. It holds everything so well, there is no guesswork.
The extra length is all behind the drivers seat. So you shorten the rocker assembly that is hidden behind the qtr panel.
Don't know why it went bold.
Yes, while I was there, I separated the rocker panel and installed 2x3 1/8 wall tube the entire length. Complete with box sections that slide into the trans crossmember through a window in the inner rocker. I wanted everything to be hidden on this car.
I have put subframe connectors in other people's cars, usually convertibles, for years. Of course all pictures are film not digital so hard to upload. I always run the connector into the rear rail, and open the transmission crossmember from the top and box the inside where the connector hits the transmember.
I put subframe connectors in my first cuda in 1980. Then added gusset plates to the rocker. Eventually triangulated under the hood. Then made a replacement rear shock crossmember.
That car is stiff. The suspension no longer flexes the car, and it rides very smooth.