I've got a 511 blk in my Malibu with 2 bolt mains and 13.5 pistons and 377" i've even welded the side of the blk about 4" crack just below the deck and put close to 150 passes on it with alcohol, no problems so far. I also have a 511 4blt main on the engine stand for a 406" street motor. If i had my ratheres they would both be Dart blks. But thet are what i have.
My main concern would be with the mismatched main caps that you have on your blk. That means line boring and tapping the extra main holes, it will cost you money to run this blk. for sure.
JMO
Zip.