The above info is pretty good. Get the car running good and drive it around for a while before you start changing things. It has to be a fun car to drive. You will probably blow off a set of tires pretty quickly. haha BTW you can get a nasty ticket or group of tickets if you aren't carefull.
I'd take a carb off and look inside the blower. Pop the belt off too and spin the blower by hand. It should turn freely and not be scored or chewed up. If it is you will definitely be down on boost. No easy or cheap fix here. You will have to send it to one of the blower shops for a rebuild.
The things are heavy. Around 70-80 pounds.
$300 up pluss massive shipping.
You can get a vacuum/boost gage from autometer in several different styles. Get one. Install the 1/8 npt fitting in the manifold under the blower. Yes there will be vacuum in the manifold even cruising. You will only get boost when the throttle is open far enough for the blower to draw in more air than the motor can by itself. The 6-71 blower displaces 411 cu in per revolution and is quite efficient at relatively low speeds. You have to overcome vacuum before you get boost. It happens pretty quick however. Don't get too carried away with boost on the street. 5-8 psi is good for a SBC You could go to 10-11 underdrive and pick up a little but I'd be carefull. The more boost you have the more critical timing and carb tuning becomes. The first time it backfires hard will open your eyes for sure.
$60 or so
Try your converter out for stall speed. You really need about 3000 stall even with the blower in this case. I've got a 3k in mine and it really made driving it more fun.
$350 or so
The 4.56 gear are going to be a major pain on the street. I ditch them for a 3.73.
$175 +/- a little. If you install them yourself.
add another $100 minimum if you don't.
Instead of messing around with the timing light trying to figure out the advance curve just take the distributor to a good performance shop and have it run on the Sun machine. Tell them you want full advance by 2000-2200 engine rpm and about 15-16 degrees of advance. Install the dizzy and set total advance at 28-30 degrees at about 3000 rpm and let the initial fall where it might. All you need to worry about is that it doesn't kick back against the starter. It shouldn't with proper C.R. With this set up and a 3k converter you will have full advance almost anytime you step on the gass.
I put a few $$$ figures in to give you and idea of the cost of blower related items. As they say "...get used to it"