What can I expect it to run?

Ah. Gotcha. Are your long blocks similar (to that Challenger)? Remember what you see as "boost" is really a representation of the restriction of the intake system vs the force of the blower. You can make 20psi and not make much power with it, or you can make 5 psi and really make some steam all depending on the quality of the top end and cam. The only experience I have with the Kenne Bells were with the Mustangs in the early 2000's and my recollection is they never made the power they were supposed to. I'm sure they've improved since then...
On the convertor - The flash is not what concerns me. That blower is not like a centrifical or turbo - it builds boost immediately so the flash will be higher anyway. What concerns me is the shell diameter and the slippage in high gear. It almost sounds like when you spoke to them you emphsized "streetable" and "street car" so you have a street convertor as a result. Not a huge problem, but a compromise in convertor can really raise the ET. It's the same thing when someone orders a race convertor for thier street car and it stalls too high and the street performance suffers...
The larger the diameter of the shell the worse the slippage above the brake stall rating. My preference would be something like an 8" with anti-ballooning plates (like a NO2 convertor). My gut says you will be trapping at a much higher rpm just because of the slippage. You'll have to report how she goes.