i had a trinity 420 big bore kit with their stage IV porting. stock stroke crank, 70mm big bore sleeves and pistons. i ran both setups with dual 35mm carbs, VF3's, and small bore in-frame shearers. the 420 BB was a good setup, it came on sooner and pulled hard. but, the 421 cub hits more violently in the mid range and pulls much harder on top. the power is in the cubs favor, even a stock stroke 68mm bore cub because of the port layout. you can get OEM jugs ported to turn good numbers, but it will cost you a bunch of money to have a good builder to do it. it will cost a lot more than the average port job. of course over all setup is key in a drag race.