Call Rob Adler at A-Team auto. Tell him what you're doing with it and he'll suggest something appropriate.
http://local.yahoo.com/info-17315130...ed-tinley-park
You might remember Rob/Randy Adler from having the fastest street car on the planet back in the late 90s. Was a 67 GTO. They now race Super Chevy Nitro Coupe.
Ditch the 4.5" stroke. It makes too much torque, especially with the roots blower. 4.25" stroke should be max or it'll be a bitch to hook up. Centrifugal blower guys can get away with longer stroke cranks because they can stage the boost. Us roots guys can't.
Donovan gear drive over Jesel belt, in case you ever decide to go to a front mag drive. Bigger carbs... Don't starve that blower for air.