settig up a tubbed rear end

i have a 72 chevy pickup with a 92 stepside bed on it.i want to put a narrowed rearend and tubb it.dont know how to go about it i imagine ill have to cut the frame and get a new section.relloate my leaf springs or come up with some other form of suppension.any help or contacts for kits would be greatly appreciated!im putting 31.50x18 tires with18 inch weld prostars with a 4.5 offset.thanks email me at kittydogone@yahoo.com.im also putting a 454 in it with a 4 speed tranny that is in it already.what all do i need to get besides a flywheel.will it bolt to my oldclutch ? do i need to relocate the tranny? tahnks again!:confused: