help me out here guys
 

i've got an 98 F150. it currently has a 4.2L 5 speed in it. im looking to drop a small block, or even a big block V8 in it. basically what im wanting to know is how big can i go without making major modifications? and when i drop a new motor and tranny in, what else am i going to have to get? drive shaft? rear end? im a good mechanic but i havent dont this big of a project yet. any adviceis great thanks