Don has laid some sterling advice on you. Step up to the plate and buy everything new from one source.

I would suggest you go to Blower Drive Service and read EVERYTHING they have written. They've been doin' this for nearly 40 years, so they have probably "been there, done that" no matter what the subject.

They suggest a small bore 6-71 for a street 350....
"There are two different 671 blowers commonly used. They are the larger diameter blower and the small diameter blower. The large bore blower (case thickness 1/2"-) is approximately 11 percent larger in volume than the small bore. The small bore blower (case thickness 3/4"+) is recommended for 370 CID engines or less for street applications. The larger bore blower is recommended for 371-500 CID engines in high performance, racing applications."
www.blowerdriveservice.com