The Dart Sportsman block is a very good choice as it is rated at 900 horse and the rear cap uses 1/2 inch hardware and we sell those blocks all machined and shipped free in the U.S. for 2395.00
Yhe Bowtie 2503 is a good foundation but is about 300 dollars more then a Dart block.
If needed we are a WD for Dart blocks and we CNC machine our blocks.