I have a Weiand 142...but its mounted on a 360" Chevy...I can make as much as 14psi...I have all the upper and lower pullies to where I can change the boost..
the Weiand "cavitates" bad close to 18,000 rpm rotor speed...I try and keep it no more than 17,000 ...what happens when you reach its limits is that the engine feels like it hit a brick wall..
as far as on a big block..yeah a bigger blower is alway better but it will still make boost...at least 10psi or more..depending on engine rpm and pullies used..if the rotors are good..
but I do have to say they were primarly designed for 6-8 psi
one more thing...from the bottom of the intake(sbc)to the top of the carb, its 11.5 inches..
I know its apples to oranges but its the blower application