as far as space the RB decks are 3/4" taller and the RB will be heavier somewhat so if you can locate a std bore 440 block that'll clean up at 30 over for reasonable money I'd have it (water) pressure checked/magnafluxed/sonic checked & get after it EDIT With your (intended) power level it might be a plan to step up to a better (aftermarket) block expecially since you dont have one on hand