My mild 605 makes 764ftlbs@3500rpm, peaks at 4800@818.4ftlbs and holds over 800 ftlbs from 4100 to 5500rpm. I think you should rethink your transmission choices. Maybe a GOOD 727 with a gearvendors overdrive.
Also at that size you'll require a raised cam block, I could be wrong but I am unaware of a gear drive or a timing chain set for that block. A belt drive isn't really street friendly, kick up a small rock or trash and a lot of real bad things can happen. Rods and camshaft lobes can become very good friends if you know what I mean. My 605 has .060 clearance between some cam lobes and rods, I use a Milodon gear drive to make sure nothing bad happens. Dave