That combination is going to need something between 3:23 and 3:91 to have any get up and go. Considering he swapped in a BBP 7.25, there is a good chance you are dealing with a gear set in the 2:4 range right now.
Also, and EXTREMELY important...you need a converter. Something in the 3500 to 4000 rpm range.
Lastly, I have found that most 4 barrel carbs are factory jetted way too fat for the Slant.
Pull your plugs and give them a look over, then consult the experts here.
We'll work with you, man. Patience and you'll get it all sorted out