chris, most blower classes limit the cid to around 526. Still that 6-71 is very small for that size or larger. If you are going to go semi serious drag motor here, then look for a good 14-71.
Blower motors make lots of low end tork, so you really dont need to build big motors like 632s and such.
I dont know much about blown fords, but if you go over to
www.promodsource.com in the teck forum there is a guy, Mike Cantor, who seems to know a fair deal about blown fords. He would be a good guy to talk to.