You been VERY patient throughout this Build my friend so listen to what they're saying and correct a few things BEFORE strapping it down.
*As said the pump "MUST" be gravity fed from the tank, THAT IS A MUST
*As for it starving for fuel after you drove it, that in itself has to be corrected before you strap down. What Fuel Pump are you running ??? I had that problem once when I used too much pump and it went into thermal overload when hot (on a different SC vehicle I had).
*As for Boost you have to remember with the Big Blowers you dont need insane boost to make insane power so I agree to Dyno it with 5 or 6.
You have to remember that the more boost you run the more octane you need. Have you done the math on yours and figured out the final compression ratio ??? My 871 is -5.5 underdriven and I'm only running 7-8 lbs of Boost and it's the equivalent of 13.1 compression ( I started with a 8.75 motor). I have The Pulley Drive Ratio Chart, The Drive & Boost Chart, The Final Compression Chart, and the Upper & Lower Pulley Charts, but it's all for the 871 so it wouldn't do you any good unfortunately.
As for the belt here you go straight from The Blower Shop and exactly how I have mine for 2 years now
The blower belt adjustment should be done with the motor cold, and have 3/4" deflection in or out on the long side of the belt. This should give you 1 1/2" total deflection. Once the motor is warm this will decrease to roughly 1/4" deflection in or out, or a total deflection of 1/2". Over tightening the belt can cause severe damage to the blower and/or crankshaft.
Here's a general final compression chart to give you an idea of how much the compression will rise with different boost levels