I'd ditch the 400 and go with a glide, much more manageable with all that BB torque. If you can fit the 12 inch rim on the car by all means use it, I've seen the shorter wall 325 fit on 12 nicely and it gets a much better contact patch. Shocks are critical on drag radial cars, double adjustable AFCO's, Strange, or QA-1. ( I listed them in price order from the most $$ to the less $$) Jim could probably point you in the right direction for the springs.
