Just MY opinion Fly... KEEP the Dart block, and stick with 23* setup...!
Once you have a Dart or World block, there is no logical reason to ever go back to a stock GM block. Get a severe duty rotating assembly as big as what can reasonably fit inside this Dart SHP block, and go with the blower on 23* top end. The blower will give you the kick in the pants you are looking for. Since you are on a budget, the 18* setup will take everything you got right up front... (just my opinion, as I have only investigated the outrageous costs, and have never bought or built anything other than 23* before).
Jim