I might be able to help some, that thermostat housing will not work, contact with the blower belt most likely..You need low compression so you are good to go there you just cant overdrive the blower a whole lot, for a big block you might want to go with a 871 or 1071.. A blower moves up about 4 psi at the same rpm every inch they add to it. (671 compared to a 871 is 1 inch so you can make 4 more psi of boost rotating at the same speed) spinning the blower faster will create more heat especially with gasoline at idle and low RPM. The blower will work great at at mid rpm, power is there as soon as you start the motor, being its crank driven (always creating boost). Your fuel mileage will be worse because you will need dual carbs and probly alot of showing off . You should be able to get 600hp as a blower should give you around 50% power gain depending on your overdrive or under drive set up (pulley sizes)... You might have been watching to many top fuel races when a normal (non radical) engine has a blower it can take a back fire if it happens alot your rotor inside the blower will contact the upper part of the case ruining your tolerances, if you are really concerned with this get a pop-off machined into the manifold or buy one with it already, but if it backfires get ready to replace gaskets as it will most likely leak (valve spring style) or if you buy the plate system have several on hand it could get expensive.. If you keep the moter simple it should be reliable not hard to start.
For blower reliabilty make sure it has hard anodized rotors and inside the case, the rotors should have teflon..........Hope that helps a little