Not sure

I dont know if this goes here but Ill try it out. I was loooking into a few cars but they have slant 6's or were a slant 6 and I was thinking about putting a small block in it. Not a 360 or 340 (to much for my blood) more like a 273 or a 318 something thats got alittle pep but still can idle in traffic and get decent mpg. But yea do I have to change out the k-member or what has to change so I can do this? And do any of you have a good low budget build for a 273 or 318? I was thinkg headers, intake, carb, and cam :-D
Thanks Nate